Chapter VI: GYMNOGENS { Cotyledons, two or (4)

The curious shapes of some exotic orchids are probably advantageous from their resemblance to insects and birds. One of our native orchids, Listua ovata, has a flower which in shape decidedly resembles a species of beetle, Grammoptera lævis, by which it is fertilized. Perhaps in this case the insect mimics the flower, as certainly happens with a pink-colored mantis in Java, which so exactly resembles a pink orchid that butterflies are attracted to it in mistake. The insect is carnivorous, and lies in wait for its prey, which is easily secured by the help of this strange disguise. Mutual resemblances of this description are rather characteristic of the Orchidaceæ. From their resemblance, real or fanciful, to butterflies, moths, bees, spiders, etc., various species of Habenaria, Neotinea, and Ophrys derive their names--the butterfly, spider, bee and fly orchises. In the orchid Ophrys muscifera are two little protuberances, regarded by the late H. Müller as pseudo-nectaries. Of this class of deceptive contrivances, however, we have a better example in Parnassia palustris, one of the saxifrages. This flower has five fan-like scales alternating with the stamens; the margins of the scales are fringed with hair-like processes, and each hair is capped with what appears to be a drop of honey. These are really hard, dry knobs, but so much do they resemble drops of honey that flies lick them before discovering the imposture. The intention of these sham nectar-drops may either be to decoy unprofitable guests from the real nectar, of which a limited supply is produced in the hollow of each scale, or to advertise it for the benefit of the more intelligent visitors.

Somewhat analogous to these pseudo-nectaries are the greenish swellings which arise on the veins of the petals of Eremurus. These little swellings present a striking resemblance to aphides, or plant-lice, and Kerner states that a fly accustomed to hunt after aphides pierces and sucks the swellings, apparently mistaking them for the insects.

Relations which remind us of the pink orchid and mantis, mentioned above, seem to exist between the little bladders of Utricularia and the entomostracans. The bladderwort is a carnivorous plant with small submerged vesicles in which minute insects and entomostracans are caught. In shape these little traps of Utricularia are not unlike the body of a crustacean; the stalk corresponds to the tail, and near the entrance of each bladder are several antenna-like filaments so resembling certain appendages of the crustaceans that they impart to the structure a ludicrous resemblance to such an entomostracan as Daphne. This curious likeness was remarked by Mr. Darwin and can hardly be altogether accidental; perhaps the prey is more readily induced to approach the snare by reason of the resemblance. Here also may be mentioned the imposture practiced on its victims by Darlingtonia, another insectivorous plant. In the hood of its pitcher-like leaf are several transparent spaces through which the light shines into the interior; to these the imprisoned flies are attracted and thereby diverted from the only opening through which escape is possible. Mistaking the “windows” for real openings, the captives exhaust themselves in vain efforts to regain their liberty and are ultimately precipitated into the depths of the pitcher.

The flowers of the ox-eye daisy and the feverfew are very much alike, and this was adduced by the late Mr. Grant Allen as a possible case of mimicry. But the probability is that in this instance the resemblance is merely homomorphic. The colors of flowers are distinctive as well as attractive. Where two species of plant grow together and are in blossom at the same time it is to their disadvantage to have the flowers of the one mistaken for those of the other. To secure cross-fertilization it is needful that the insect visitors pass from one flower to another of the same species, otherwise the pollen will be conveyed to the stigmas of the wrong species. It is of importance that the fertilizing agents should be able readily to distinguish different flowers, and this is no doubt one reason for the diversity of their colors, shapes, and odors. This circumstance must operate as a check against the production of mimetic blossoms; it will not, however, prevent flowers from acquiring a likeness to any object other than a flower.

Mimetic resemblances are much more numerous among fruits and seeds than in flowers. A very curious example is Orphicaryon paradoxum, the snake-nut of Demerara, inside which is the coiled embryo resembling a small snake. Among others mentioned by Lord Avebury are Tricosanthes anguina, the pod of which assumes a snake-like guise; Scorpiurus vermiculata, with pods in the form of a worm or caterpillar; S. subvillosa and Biserrula pelecinus, where the resemblance is to a centipede and certain lupines with spider-like seeds. The seeds of Abrus precatorius, Martynia diandra, Jatropha, the castor oil plant and the scarlet runner mimic certain beetles. The presence of a caruncle representing the head of the insect renders the imitation more complete; this structure takes no part in germination, and Kerner is of opinion that it prevents the ants from attacking the substance of the seeds which they drag about from place to place. The ox-tongue and cow-wheat have worm-like seeds, and several plants have fruit difficult to distinguish from little pieces of dry twig. The jet-black, shining seeds and achenes of Delphinium, Helleborus, Juncus, Atriplex, Polygonum, etc., are easily mistaken for beetles; the brightly colored seeds of Iris Germanica are also in all probability mimetic.

The beautiful glossy scarlet and black piebald seeds of Abrus known as rosary beans perhaps escape destruction through birds mistaking them for some nauseous insect gaudily attired in warning colors. But from the manner in which the seed-vessels of Iris and Arbus dehisce and expose their seeds the brilliant colors of the latter would appear to subserve dissemination rather than protection. Such hard seeds are probably dispersed through the agency of insectivorous birds, which seize them in mistake for their more legitimate prey. According to Lord Avebury, the beans of Abrus mimic the beetle Artemis circumusta. The smaller seeds, known as crab’s eyes, are colored in an analogous manner. These cases are the less surprising if we have regard to the fact that the majority of dry fruits, though green while growing, become black or brown when they fall to the ground, so that their general tint corresponds with their surroundings and tends to concealment.

The odors of fungi are very varied. Clathrus and Phallus are offensive and attract swarms of blow-flies; Lactarius and Hydnum, on the other hand, are sweetly scented like the flowers of Melilotus. Among the odors of fungi enumerated by Dr. Plowright are those of aniseed, mint, peppermint, garlic, horse-radish, cucumber, ripe apricots, rotting pears, rancid herring, Russia leather, gas-tar, prussic acid, nitric acid, and cacodyl. Like the hemlock, Agaricus incanus has the smell of mice, two species of Lactarius have the odor of the common house-bug, while Hygrophorus cossus smells like the larvæ of the goat-moth. Fifteen or sixteen species of agaric resemble oatmeal both in taste and smell, Hydnum repandum has the flavor of oysters, recalling the oyster plant among the Boraginaceæ, whose leaves have a similar taste. Several are possessed of a nut-like flavor. The common stinkhorn, Phallus impudicus, is the best known representative of a large family of fungi, the members of which are found in various parts of the world. The Phalloidi include Phallus, Lysurus, Simblum, Clathrus, Aseröe, and other genera, all characterized by offensive odors and conspicuous colors. These fungi have been carefully studied by Mr. T. Wemys Fulton, whose paper on the _Dispersion of Spores in Fungi_ in the _Annals of Botany_ for 1899 contains many interesting and important observations bearing on mimicry.

The rapid elongation of the stinkhorn is very remarkable; the fungus has been observed to attain a height of several inches in half an hour, furnishing an apt illustration of the proverb that ill weeds grow apace. It not only emits an intolerable charnel-house stench, but its ghastly pallid hue seen against the background of its usual surroundings is peculiarly suggestive of the dead carcass of some animal. Its surface at first exudes a sweetish slime containing sugar, but the hymeneum or spore-bearing portion is deliquescent and the entire mass speedily undergoes a series of changes, the white becoming brown, then black, the solid mass being ultimately resolved into a dark fetid fluid in which the spores are suspended. These mimetic changes, which so closely approximate to those of decomposition, attract carrion flies in prodigious numbers. Blow-flies even deposit their eggs on the fungus, and the maggots seem to develop as though nourished by its substance. On examination Mr. Fulton found the spores adhering in thousands to the feet and proboscides of the insects. Their excrement he found to consist almost entirely of spores, and the latter were found by experiment to be still capable of germination. There is therefore no doubt in this case that flies are employed as agents in the dispersion of the fungus. This statement also applies to various Coprini and others with a deliquescent hymeneum.

Quite a number of flowers have distinctly mimetic odors. It can hardly be doubted, for example, that the offensive smell of the carrion flowers Stapelia, Aristolochia, Arum, Rafflesia, and others, is more effective in promoting cross-fertilization because of its resemblance to the odor of putrid meat. So completely are the flesh flies deceived that they often deposit their eggs on the petals of carrion flowers.

Fetid odors occur in Bryonia, Helleborus, Geranium, Stachys, Ballota, Iris and other genera. The odors of others have a curious resemblance to the smells emitted by certain animals. Hypericum hircinum and Orchis hircina are bad smelling flowers with an odor resembling that of the goat; Coriandrum sativum has the fetid smell of bugs, while the hemlock, again, emits a strong odor of mice. Along with these may be mentioned Adoxa, the musk orchis, the grape hyacinth, and other musky-scented flowers.

The resemblance in smell between these flowers and the secretion formed in the scent glands of the musk ox and other animals is, to say the least, a remarkable coincidence. Possibly flies which accompany cattle may be attracted by smells of this description. Very curious also is the vinous smell of Œnanthe, and the brandy-like aroma of the yellow water lily Nuphar, hence called the brandy bottle. Ethereal oils exhaled by plants while attractive to some animals seem to repel others; the scents of sweet-smelling flowers such as Daphne, Thymus, Marjoram, Melilotus, and Gymnademia, though grateful to bees and butterflies, appear to be distasteful to ruminants. Kerner states that in general the latter avoid all blossoms; even caterpillars do not readily attack the petals of their food plants. Odor may therefore be protective or attractive or it may be of use in both ways. The same remark applies to color, which may serve either to attract or repel; the richly variegated leaves of the Indian nettles--species of Colleus--and the tinted foliage of begonia and geranium may possibly escape injury on account of the general resemblance to colored blossoms. Instances in which one plant resembles another in smell are not very common in the flowering class, though cases do occur like the garlic, mustard and apple-scented Salvia. Resembling odors are much more frequent among fungi.

Characteristic examples of homomorphism are seen in the resemblances which many species of Euphorbia present to the cactus tribe and in the pollen-masses of the orchids and asclepias. In Britain the order Euphorbiaceæ is represented by the box, dog’s-mercury, and the sun-spurges, but many foreign species have quite a different appearance and agree with the cacti in their aborted leaves and green succulent stems. The globular, columnar, and angular forms give to both a peculiar aspect by which they are broadly distinguished from all other vegetable types; and yet in systematic position these two orders stand far apart. The nearest affinities of the Euphorbiæ are with the Urticaceæ and other orders having incomplete flowers, while the nearest allies of the Cacti are the Cucurbitaceæ and other calycifloral orders. Succulent stemmed plants of this description are specially adapted to an arid climate, and it is not unreasonable to suppose that the similarity between the Euphorbiæ and Cacti results from the long-continued action of similar external conditions upon similarly endowed tissues.

The Australian Casuarinas are dicotyledons with incomplete flowers nearly related to the oak, hazel, and other Cupuliferæ, but in outward appearance they have a singular resemblance to the horsetails, a family of cryptogams. One of the gymosperms or cone-bearing class, Ephedra, also presents the same jointed appearance so characteristic of Equisetaceæ. Growing in marshy places very like those affected by Equisetum we find the mare’s-tail Hippurus, a flowering plant allied to the fuchsia family, but externally resembling Equisetum in its jointed stem and whorled leaves. A familiar instance of the same kind of homomorphism is Equisetum sylvaticum, which might almost be described as a liliputian fir-tree. The little flowers of the water ranunculus look exactly like miniature water lilies, while the leaves and flowers of Caltha palustris simulate the yellow Nuphar so much that in some parts of the country the marsh marigold is known as the water lily. The specific name of another aquatic, Lymnanthemum nymphædides, indicates a peculiarity of the same kind. Leaf analogies are frequent among aquatic plants; the orbicular, peltate leaf of the Indian cress occurs, for example, in Hydrocotyle, Nelumbium, and others. The brown color and translucence of Potamogeton, Myriophyllum, and other aquatics assimilates them to the fronds of Laminaria and other sea-weeds.

A grass-like habit is assumed by some plants. This character is attained in the meadow vetchling by the arrested development of the compound leaves and the great elongation of the stipules. Lathyrus nissolia has the stipules minute, but the phyllodes or leaf-like petioles impart the grass-like character. A moss-like habit occurs in a great many plants belonging to very different families; thus the wiry stem of the purging flax reminds one of the seta of Polytrichum. The pearlwort of the walls, many alpine saxifrages, pinks, and gentians present very much the appearance of mosses, _e. g._, Silene acaulis, Saxifraga bryoides, S. hypnoides, Arenaria Cherleri, etc. The sub-species Saxifraga geum is another instance of leaf analogy. The generic name Pyrola implies a fancied resemblance of the leaves to those of the pear tree. Certain leaf-types frequently recur, the rough broadly tongue-shaped leaf of the bugloss, for example; hence the very common specific appellation echioides. The nettle-leaved bell-flower reproduces the foliage of Urtica and the sinuate leaf of the oak appears in several families.

Parasitic phanerogams like Rafflesia commonly exhibit the fungoid character in a marked degree. In their internal structure, coloring, spore-like seeds and other characters they approximate closely to the fungi.

As examples of homomorphism between closely allied plants may be mentioned the false oat, which so strikingly resembles the cultivated species, and the barren strawberry, which agrees so closely with the cultivated strawberry of our gardens.

Although it is only under exceptional circumstances that a flower is likely to mimic another blossom closely, vague general resemblances are not uncommon, such as that between the rock-rose and the buttercup, between the milkwort and the vetch, and between Veronica and Valerianella. A more decided likeness is that of the garden annual Collinsia to the butterfly blossoms of the pea tribe. This case is peculiarly instructive since the homomorphism can be traced to its cause. The butterfly-like corolla of Leguminosæ seems to have afforded the pattern after which a number of flowers have been fashioned. The Papilionaceæ are adapted to bees rather than to butterflies or moths, and the pollen is applied to the ventral surface of the insect, the essential organs being lodged in the carina or pouch formed by the two lower petals. Among the Scrophulariaceæ to which Collinsia belongs, the pollen is commonly sprinkled on the back of the insect and the stamens are contained in the upper lip of the corolla; Collinsia is, however, exceptional; the stamens are lodged within the lower lip of the flower and the pollen is applied to the ventral surface of the bee. Here the resemblance is evidently an indirect result brought about by the flowers of Collinsia having become adapted to the same class of visitors as the Papilionaceæ, viz., bees which have their brushes or baskets of hair for collecting pollen attached to the abdomen. Where two flowers are very like insects are apt to mistake the one species for the other, but this will not involve any loss if there is an interval between their periods of blossoming.

Homomorphic likenesses are not confined to homologous organs; an organ of one plant sometimes exhibits a perfect resemblance to a different organ on some other plant. Thus Aristolochia sipho, the Dutchman’s pipe, so-called from the appearance of its flowers, has a perianth singularly like the leaf-pitchers of Nepenthes, and the curious little nectaries of Nigella might almost be compared with the pitchers of the Australian insectivorous plant Cephalotus. As the Aristolochias imprison small dipterous insects in their flowers these instances favor to some extent Henslow’s idea that both flowers and pitchers have arisen by hypertrophy caused through the irritation set up by insects.

The homomorphism of the orchids and asclepiads is especially interesting because of the objection to the Darwinian theory that it presents; the coincidence is certainly unfavorable to the notion of fortuitous variation. The orchids and asclepiads agree in producing pollinia or pollen-packets which attach themselves to the bodies of insects and are thus transferred from flower to flower. Although the two flowers differ greatly in the details of their structure, this curious contrivance occurs in no other plants, and yet the two orders are as widely separated as it is possible to conceive. The orchids belong to the petaloid division of Monocotyledons; the asclepias to the gamopetalous Dicotyledons, with their nearest allies among the Apocynaceæ, of which Vinca, the periwinkle, is perhaps the best known representative. Although agreeing in this one particular, the flowers are in other respects very dissimilar.

Another contrivance for promoting cross-fertilization met with in unallied plants is the mouse-trap arrangement of hairs by means of which small flies are temporarily imprisoned. This arrangement occurs in Aristolochia, in species of Arum, and in Ceropegia, one of the asclepiads. In these plants, where the affinities are so slight, the mechanism for fertilization must in each case have arisen independently.

THE BAMBOO AND PLANT GROWTH
--R. CAMPER DAY

If the many families of flowering plants were arranged in the order of their utility to man or in the order of their abundance, the first place in the list would unquestionably be assigned to the great family of grasses. Of their omnipresence and abundance some idea may be obtained from the fact that at least four thousand different kinds have been described, and a German naturalist has estimated that they constitute a twenty-second part of all known plants. Their utility as food producers becomes obvious as soon as we recall the names of rice, wheat, barley, oats, rye, and Indian corn, and remember how large a proportion of our food is made from their seeds. Most of these civilized and somewhat unnatural grasses have been so long under cultivation, and so much altered by man’s selection, that they are totally unfitted to shift for themselves, and would soon become extinct if brought into competition with wild plants. The fact that the wild forms from which they are descended can not now be identified with certainty shows that their cultivation must date from the very earliest ages. Rice alone is said to furnish more sustenance to the human race than any other single species; the common meadow grasses, such as the purple-tipped Anthoxanthum, which fills the fields with its penetrating fragrance when the hay is newly mown, are almost the only food of sheep and cattle; and those tall and sturdy canes whose juice we squeeze out between rollers, and clarify and crystallize into sugar, are only modified stems of grass.

The largest of the family, and perhaps the most beautiful, is the tropical arborescent grass which bears the name of bamboo. Although it is not cultivated for the sake of its seed, it has many admirable qualities, and wherever it grows in abundance it is applied to a variety of uses. “The strength, lightness, smoothness, straightness, roundness, and hollowness of the bamboo,” says Mr. A. R. Wallace in his _Malay Archipelago_, “the facility and regularity with which they can be split, their many different sizes, the varying length of their joints, the ease with which they can be cut and with which holes can be made through them, their hardness outside, their freedom from any pronounced taste or smell, their great abundance, and the rapidity of their growth and increase, are all qualities which render them useful for a hundred different purposes, to serve which other materials would require much more labor and preparation. The bamboo is one of the most wonderful and beautiful productions of the tropics, and one of nature’s most valuable gifts to uncivilized man.”

In order that the accuracy of this eulogy may be appreciated, let us imagine the case of a shipwrecked man landing without any tools, except an axe and a knife, upon an island in which we will suppose the bamboos are the only vegetation, and let us see how far he could supply his needs with their assistance. One of his first requirements would be a house, and this could be provided with very little labor. The stems of one of the larger species, such as Bambusa Brandisii, driven into the ground, would form excellent uprights for the framework, which could be completed with lighter cross-pieces nailed to the uprights with pegs of the same material. A good roof could be made by taking broad strips split from large bamboos, and fastening them side by side with their concave surfaces uppermost, the interstices between them being covered with other pieces having their convex sides uppermost. Similar but flatter pieces laid upon the joists, and tied down firmly with strips shredded from the outer rind, would form a smooth and elastic floor such as could not be made out of other materials without a great expenditure of labor. Thin strips plaited together, or broad strips pegged side by side, might be used for the walls.

The furnishing of the house would be an easy matter, for bedsteads, chairs, brooms, baskets, cords, fans, bottles, mats, and hoes can be made of bamboo with the greatest facility. The water-tight joints of the stems form admirable water-vessels, and it would be easy to bring the water to the very door by a gently sloping aqueduct of pieces of bamboo split down the middle and supported at intervals on cross-pieces arranged like the letter X. The jars made from the joints could be utilized not only for holding water, but even for boiling it. Mr. Wallace tells us that rice, fish, and vegetables can be boiled in them to perfection. The young shoots of the bamboo as they first spring from the ground are said to be a delicious vegetable, “quite equal to artichokes.” That fish may be readily caught by the agency of the bamboo is shown by the many specimens of ingenious fish-traps exhibited in the museum at Kew. If we suppose our adventurer to take a thin stem of bamboo, and cut off the end obliquely just above a joint so as to leave a sharp edge, he would be provided with a hard-pointed and very efficient spear. In the same way he could supply himself with daggers and arrows; while from the more elastic species he could make himself a bow, using a thin strip of the outer rind for a bow-string. The lowest internode of Arthrosylidium Schomburgkii, which sometimes attains the extraordinary length of sixteen feet, far surpassing the length of the joints in all other bamboos (says General Munro), furnishes the “Sarbican” or blow-pipe through which poisoned arrows are blown by the natives of Guiana. In the island of Celebes the only article of dress worn by the natives is a body-cloth called Kian Pakkian, made of bamboo split into fine shreds, which are passed between the teeth and bitten until they are soft, when they are woven.

If, after providing himself with these and similar necessaries, our shipwrecked man found leisure to amuse himself, he might make æolian flutes, such as Sir Emerson Tennant saw in Malacca, by boring holes in the stems of living bamboos, or he might construct a harp like that in the Kew Museum, London, which was brought from Timor by Mr. Wallace. This harp is made from a cylinder of bamboo having a node at each end. Under a strip of the outer rind a quarter of an inch wide, a sharp knife is passed so that the strip is detached from the cylinder except at its two ends. The strip forms one of the harp strings. Two small wedges are pushed under it, and the portion between the wedges can be sounded like the string of a guitar. It is also possible, and not very difficult, to make such diverse articles as paper, pens, waterproof clothing, hats, wax, pickles, bird-whistles, rafts, pillows, fermented drink, and bridges from the same versatile vegetable. In the Kew Museum, which should be visited by every one who wishes to see the varied uses to which bamboos can be applied, perhaps the most curious article is a headman’s knife brought by Mr. Franks from the southeastern peninsula of New Guinea. This singular implement, which is shaped like a cheese-scoop and seems very ill-adapted to its purpose, is marked with numerous notches, each notch representing one of its victims; and it is accompanied by an artistic apparatus, also of bamboo, intended apparently to enable the executioner to carry the severed head.

The bamboo usually grows in a cluster of from ten to a hundred stalks, and springing from the same rhizome or root-stock. The rhizome is not the root, but an underground portion of the stem. It consists of a number of segments about the size and shape of a banana and somewhat bloated in the middle. The banana-like segments are joined together irregularly by their tips, so that the whole rhizome forms a strong underground trellis-work admirably adapted to support the light and yet rigid stems that rise up from it. From the under side of the rhizome spring downward the true root-fibres, numerous as the bristles of a broom.

The stem itself, as every one knows, is smooth, polished, and cylindrical, and is divided into air-tight compartments by knots or nodes, which are the points at which the fibres of the stem cross over from one side to the other. The lowest ten nodes or so are usually bare, but from the upper nodes issue branches. These are very slender as compared with the main stem, and carry the foliage leaves. In most species the leaves are rather small, but in some they are very large. The species named Planotia nobilis by General Munro, a native of New Granada, has the largest leaves of any kind of grass; they are often a foot in diameter and fifteen feet in length.

The most important part of the bamboo, from a botanical point of view, is the flower, which roughly resembles the flower of our common grasses. The flower of grass is inclosed in hard, scaly leaflets called glumes; it usually has three stamens and one seed-vessel. There may be only one flower inclosed in the glumes (as in foxtail grass), or more (as in wheat). The flowers of the bamboos, while on the whole conforming to the grass type, exhibit many small differences in different species. In some kinds, as in Arthrostylidium longiflorum, the inflorescence resembles a bunch of ears of wheat; in others, as in Bambusa vulgaris, the flowers are packed into round clusters; in others, as in Chusquea simpliciflora, they are in threes and fours, each flower hanging by a separate slender stalk. The seed generally resembles oats or wheat, but in some species it takes the form of a berry, not unlike the seed of our familiar pimpernels. In the species known as Molocanna, the fruit is exceptionally developed, often attaining the size of a largish pear. Some species flower and die down annually; others flower annually, but live on; as a rule the bamboo grows for many years without flowering, and then suddenly bursts into bloom. From the fact that the number of years between the sowing of the seed and the flowering of the plant varies, and that in some years nearly all the bamboos in a given district flower simultaneously, it would seem as if the blossoming does not take place at any prescribed age, but may occur at any period after the plants reach maturity when a favorable season supervenes. It used to be thought that after a general flowering of the bamboos throughout a district all the plants died, but this view proves to be incorrect. The flowering shoots usually die, and during the flowering the foliage almost entirely disappears, but the entire plant is not necessarily killed.

The Chinese have a proverb that the bamboo produces seed most abundantly in years when the rice crop fails, and several curious cases of the truth of this saying have been recorded. According to General Munro, in 1812 the universal flowering in Orissa prevented a famine. Hundreds of people, he says, were on the watch day and night to secure the seeds as they fell from the branches. Another instance occurred in 1864, when there was a general flowering of the bamboo in the Soopa jungles, and very large numbers of persons came from the neighboring districts to collect the seeds.

In most bamboos, the stem is characterized by straightness, smoothness, roundness, and quickness of growth, no doubt because these qualities have, as a rule, proved serviceable to the plant in the struggle for existence. Light and air being necessary to the life of grass, it is manifest that in the dense vegetation of the tropics a plant which can push itself rapidly to a great height must have an advantage; and in order that growth may be rapid and the plant spring up to a considerable height without climbing, it is essential that there should be as little material as possible in the stem, and yet that it should be as strong as possible. It is difficult to imagine a stem in which these conditions would be better fulfilled than in that of the bamboo. By reason of its hollowness the amount of material is reduced to a minimum; and by reason of its cylindrical shape, its nodes, and the hardness of the outer rind, the strength of the structure is at a maximum. The growth is consequently very rapid, an increase in height of 2 to 2½ feet having been recorded in a single day. The Bambusa Brandisii often measures as many as 120 feet, and is said to attain its full altitude in a few months.

But although, as a general rule, the necessities of natural selection have ordained that bamboos shall be perfectly straight and perfectly round, this archetypal form or idea (to borrow a word from Plato) does not always hold good. One species, found in Asia, is said to have crooked and even creeping stems. Another, found in Ecuador, is described by General Munro as being distinctly a climbing plant. There is a species, recently described by Mr. Thiselton Dyer, with a stem exactly square, and as well defined as if cut with a knife. It has only lately been found in China, where it is grown chiefly for ornament.

According to Mr. Dyer, the Chinese account for its squareness in the following way. They say that in the Fourth Century A. D., the famous alchemist, Ko Hung, took his chopsticks (which consist of slender rods of bamboo pared square) and thrust them into the ground of the spiritual monastery near Mingpo; and then by his thaumaturgical art he caused them to take root and appear as a new variety--the square bamboo.

The growth of plants is one of the greatest mysteries of nature, and nothing is more mysterious in their growth than their limited but very definite power of movement. How is it that some plants grow vertically upward, like the normal bamboo, others climb and twist, others creep, and others grow in zigzag shapes? How is it that some turn toward the light, some away from the light, while others place themselves at right angles to it? And how is it that if you peg down the young stem of a vertically growing plant it will bend upward beyond the peg? No doubt the proximate cause is natural selection; they do these things because they have found them advantageous. But this does not tell us by what mechanism a plant is enabled to keep on growing in the particular direction which it finds advantageous. We know that when a plant bends in a given direction, the cells on the convex side of the bend are more turgescent, that is, more distended with sap, than those on the concave side, and that the increased turgescence of the former is followed by increased rapidity of growth; but what causes the distribution of turgescence in the cells has not been clearly made out. It seems probable, however, that when a shoot is growing in its proper and natural direction, the chief force which guides it and enables it to maintain that direction is the force of gravitation. To this force the growing portions of a plant are extremely sensitive. Consider, for example, the case of a vertically growing shoot. Whenever it is accidentally bent the force of gravity must evidently act upon the portion above the bend, tending to curve it still more, and causing a strain in the material of the stem. The plant in some mysterious way is aware of this strain, and the cells of the lower side of the bent portion are stimulated to increased turgescence as compared with those of the upper side, so that the under side would grow faster; and as the plant would turn upward in consequence, any deviation from the perpendicular would tend to correct itself. Similarly a shoot which grows horizontally is led by the same stimulus of gravitation to rectify any departure from a horizontal position. Gravitation, then, does not _cause_ the bending when a displaced shoot endeavors to regain its normal direction, but serves merely as a guide. By its means the plant is made aware (so to speak) that it has been displaced, and takes measures accordingly. If the force of gravity were absent, the shoot would go on growing in any position in which it might happen to be placed. This may be proved by causing a growing seed to revolve slowly round a horizontal axis, so that at every revolution the force of gravity may act upon it equally in all directions. When a shoot is grown in these conditions, it is found that its power of correcting deviations from any particular line of growth is lost. Similar reasoning applies to the action of light on plants, but, as above stated, we do not know why it is that plants respond to the stimulus of light or gravity; we only know that as a matter of fact they do so.

It has often been vaguely asserted that plants are distinguished from animals by not having the power of movement. It should rather be said that plants acquire and display this power only when it is of some advantage to them; but that this is of comparatively rare occurrence, as they are affixed to the ground, and food is brought to them by the wind and rain. We see how high in the scale of organization the plant may rise when we look at one of the more perfect tendril-bearers. It first places its tendrils ready for action, as a polypus places its tentacula. If the tendril be displaced, it is acted on by the force of gravity and rights itself. It is acted on by the light, and bends toward or from it, or disregards it, whichever may be most advantageous. During several days, the tendril or internodes, or both, spontaneously revolve with a steady motion. The tendril strikes some object, and quickly curls round and firmly grasps it. In the course of some hours it contracts into a spire, dragging up the stem and forming an excellent spring. All movements now cease. By growth the tissues soon become wonderfully strong and durable. The tendril has done its work, and done it in an admirable manner.

THE REIGN OF EVERGREENS
--GRANT ALLEN

The poor stripped and draggled garden is beginning to look very bare now (November) of all except a few straggling late-flowering shrubs and those trusty adopted friends that we have always with us, the shrubby, large-leaved southern evergreens. In northern climates, we must ruefully admit, there are hardly any true evergreens, save only the conifers, with their stiff and needle-like foliage, such as pines and spruce-firs; but we make up for it to some extent by borrowing from warmer or more southern lands the laurels, aucubas, laurustinuses and rhododendrons, that help to keep bright our English lawns and shrubberies throughout the long and weary winter months. Indeed, our only native flat-leaved shrubs that retain their full greenness from year’s end to year’s end are privet, box, and butcher’s broom, all three of them very doubtfully indigenous to these islands. It is the rule with English trees and shrubs to shed their foliage every autumn; and the fashion in which they do so shows very clearly how purposive and well adapted to their conditions in life is the deciduous habit. For the leaves do not merely tumble off anyhow, casually, before the first fierce autumnal winds; if they did so there would be loss of sap and of valuable foodstuffs to the whole plant of whose joint commonwealth they form the partially dependent members: their fall is duly provided for beforehand, and when at last it actually takes place, it takes place in an orderly and regular fashion, with the least possible injury to the interests of the entire tree. From the very beginning there has been arranged at the joint where the leaf-stalk joins the stem, or where the separate leaflets join the central midrib, a row or articulation composed of cellular tissue, and specially designed to act as a joint for the dry leaves. When winter approaches, and chilly northern winds are likely to tear to pieces the leaves on the trees, all the protoplasm and other valuable cell-contents are withdrawn into the permanent tissues of the plant, leaving only the minor red and yellow coloring matters (mostly effete and used-up foodstuffs) which give so much beauty and glory to the general aspect of our autumn woodlands.

Then the articulation dries up and withers, and the dead leaf separates at the joint, leaving behind it a regular mark or scar, which is the visible token of Nature’s definite precaution against the northern cold and tempests.

It was not always so, however, and it is not so even now in the greater part of the modern world that we ourselves inhabit. It seems quite natural to us northerners that “leaves have their time to fall”; so natural, indeed, that we almost forget the strict limitation of the practice to our own chillier latitudes. Yet in reality the existence of deciduous trees is a mere temporary accident of the here and the now, a passing consequence of the great cold spell which had its culminating point in the last glacial epoch, and from whose lasting effects we ourselves are even still apparently suffering. Whether, as Mr. Alfred Russel Wallace seems hopeful enough to believe, our poor old planet may yet recover from this premonitory chilling or not, whether we may yet look forward to a few more warm spells or otherwise, before the final numbness of all dying worlds comes upon us, is a question rather for the consideration of astronomers and physicists than the mere mundane-roving naturalist, with his petty ephemeral interests in our plants and animals; but one thing at least is certain, that till a very recent period, geologically speaking, our earth enjoyed a warm and genial climate up to the poles themselves, and that all its vegetation was everywhere evergreen, of much the same type as that which now prevails in the modern tropics. Indeed, we have only to look at the existing state of things in order to see how very slight is the effect that has thus been produced upon our temperate flora. For example, among the oaks alone, there are some twenty species in Europe, of which Southern Europe has eighteen, mostly evergreen, while north of the Alps there are only two, or at most three, all of them deciduous. From the evolutionary point of view it is clear that the northern kinds are modern developments, specialized to contend with the peculiarly cold conditions of sub-Arctic Europe.

Fortunately, too, we are not left in this matter to mere conjecture or analogy: thanks to the researches of Heer and others, we have positive geological facts to guide us which show conclusively that up to the Miocene period Europe was covered by forests of large-leaved evergreen trees, of what we should now consider distinctively tropical types. Ever since the Miocene, and on to the culminating point of the great Ice Age, the European climate has been growing steadily colder, and the European flora has been at the same time steadily adapting itself to the new conditions, and to assuming what we now consider a typically northern aspect. During all that time, the large-leaved evergreens gave way before the deciduous trees and the chillier conifers, beginning at the north pole and spreading gradually southward, as the cold deepened and widened its range. Since the end of the great Ice Age, and the subsequent slight amelioration of the climate in Northern Europe, a reverse process has begun to set in; the Arctic types have begun to recede slightly once more, and the comparatively southern or temperate types have pushed their way northward to occupy the place from which they were previously dispossessed by the newly evolved kinds. It is not necessary for us to inquire here into the causes of this great cycle; the facts are there, and for our present purpose they are quite sufficient. They show conclusively, when one follows them out in detail, that the evolution of deciduous trees was concomitant with the growth of cold conditions around the two poles; and that such trees now exist only where winter, for part of the year, renders the evergreen condition an undesirable one. Even in the tropics, indeed, we find on high mountains a belt of deciduous forest, stretching above the belt of large-leaved evergreens, which itself succeeds to the lowland palms and tree-ferns of the thorough-going equatorial plains.

The reason for the evolution of deciduous trees is of course to be found in the peculiar circumstances of the circumpolar regions. In the tropics, trees and plants can thrive and blossom all the year round; and even in temperate countries most small herbs and weeds gain by keeping their foliage throughout the winter; but big trees in cold climates would suffer much by the tearing and strewing of their leaves in winter gales, while they would obtain little advantage by retaining them on the tree during the long chilly season. Hence, if any tree happened to possess any arrangement by which dead or dying leaves could be removed without injury to the permanent tissues, while, at the same time, the useful materials were withdrawn into the young bark to await the spring awakening, such a tree would obviously enjoy an advantage in the struggle for existence, and would be likely to outstrip its evergreen neighbors in rigorous climates. Now, as a matter of fact, the germ of such an arrangement is found even in many herbs or small shrubs, such as, for example, the common pelargoniums or “scarlet geraniums” of our flower-gardens. Everybody who has ever kept these familiar plants in his own rooms must have noticed how easily the dead leaves separate from the stem at their base, by means of the swollen cellular mass where the leaf-stalk joins the axis. All that the forest trees of northern climates had to do, then, was just to take advantage of this nascent provision, wherever it existed (mark this prior necessity), and render it more fixed under the influence of natural selection. But if we may judge by the actual sequel, it was not every kind of tree that could adapt itself to the altered circumstances; as a matter of fact, the number of species among northern forest trees is very small indeed, and even out of this small number a good many are conifers, like the pines and yews, whose narrow tough leaves are well fitted for withstanding and battling against all the winter breezes. Still, among the conifers themselves there are a few species, such as the larches, with tender, delicate foliage, which have also become deciduous under stress of altered conditions. At the present day the large-leaved and flat-leaved evergreens are mostly confined to tropical, sub-tropical, or at least warm temperate climates, and all the forest trees or the circumpolar tracts are either deciduous, or else are tough leathery-leafed conifers. The laurels and rhododendrons, with which we strive artificially to brighten up our comparatively leafless English winter, are either hardy representatives of the warm temperate flora, or else mountain species from southern climates, with constitutions just strong enough to endure our chilly season in favored and carefully selected situations. Such evergreens have generally very rigid and shiny leaves to protect them--a point well marked in ivy and laurel as compared with Virginia creeper and English hawthorn.

OUR MICROSCOPIC FOES
--A. WINKELRIED WILLIAMS

Of all the foes that are waging war against mankind, the most dangerous and deadly are minute organisms belonging to the lowest order of plant-life, and invisible to our naked eye. An immense number of these always surround us, and are ready to make an attack should they find a weak point in our defences.

Their presence in the air may be readily demonstrated by exposing some material upon which they can feed, and watching the result. The simplest method is to boil a potato, cut it in half, and immediately place one-half under a bell glass purified by being washed in an antiseptic solution such as corrosive sublimate. Expose the second half to the open air for a short time, and place it also under a glass. Let them remain for a few days, and then examine. If the first half has been placed rapidly enough under the glass, we shall find it unaltered. On the second half, however, we shall see a number of small but growing spots, which will probably vary much in color. These consist of colonies made up by immense numbers of most minute plants, _i. e._, bacteria, and also of higher fungi. Certain species of the bacteria constitute our dreaded foes.

Bacteria are non-nucleated unicellular plants, which may be roughly classed into two divisions according to their shape, the circular forms being called micrococci, the elongated forms bacilli. In size, they are most minute, being only visible under the highest powers of the microscope. Many are provided with cilia, by the lashing of which they are capable of independent movement. They are composed of a peculiarly resistant protoplasm, which is condensed at the surface, so that by the action of certain caustics they can be separated from many tissues on which they may be lying, the caustics destroying these tissues.

Bacteria have enormous power of reproduction, which is accomplished by division of the cells and fission. Many also form globular spores by a condensation of their protoplasm. The spores have a much higher power of resistance than the bacteria themselves, and may under unfavorable circumstances be quiescent while awaiting better times to take on full development.

Their _habitat_ is almost everywhere. In water, bacteria exist in great numbers; they are even found in springs at their sources. This indicates their presence in the soil, where they are found in great numbers. We have already seen that they exist in the air, but being, for their size, heavy bodies, they are invariably attached to less dense particles of dust. Out at sea, we find the air free from bacteria, although in the water they abound. The higher we ascend, the fewer we find. In towns, the air teems with them; in the country but few exist. In the healthy living body, there are no bacteria, except in the alimentary canal and upper respiratory passages. It must not be supposed that all bacteria are the forerunners of disease; such is the case with only certain forms to which the significant term pathogenic bacteria is applied. Many authorities assert that the non-pathogenic forms may, under certain circumstances, develop into pathogenic forms. This, however, has not been definitely settled, since we are only able to separate the different classes of bacteria by their action on cultivating media and on the living body. We have not yet been able to develop by cultivation a virulent form from a non-virulent, although we have by repeated cultivation diminished the virulence of the most malignant bacteria.

Of all the pathogenic bacteria we have the most direful tale to tell. Of one, discovered by Dr. R. Koch--namely, that of tubercle--the terrible ravages on human life by ferocious animals in India (over 24,800 fatalities per annum) are but trifling compared to the ravages stealthily done in our midst by this the smallest of the class of most minute living units. According to Dr. Koch’s estimate one-seventh of the human race die of pulmonary consumption, and this is only one, certainly the most prolific, of the many diseases directly caused by the tubercle bacillus.

Happily for warm-blooded animals, these terrible death-dealers differ from most other bacteria, for although they can remain alive for some time outside the body, they are unable to develop in the outside world, and this considerably limits their number. A temperature above 96° Fahr. is necessary for their growth, and there are only a very few soils on which they can be cultivated, such as blood-serum and meat jelly. Moreover, they develop more slowly than other known bacteria, which may consequently outgrow them, and prevent their development. How, then, are we to account for the fact that tubercle is such a widely spread disease, not only among all the races of men, but also among many of the lower animals? The consideration of the following facts answers this question.

The tubercle bacillus can form resting spores; consequently, when once the tissues of a part have their vitality so lowered that the entrance of the bacilli is allowed, they can retain their hold with great tenacity. Although the bacilli can not develop outside the body, their vitality is preserved for a long time. Certain animal products used for food, such as the milk of tubercular cows, contain the bacilli. Experiments such as causing animals to inhale the tubercle bacilli, or the introduction of them into the blood, or sometimes the feeding on tubercular matter, result in tuberculosis.

Pulmonary consumption presents an example of the most typical way in which the tubercle bacillus performs its deadly work. In the majority of cases, the bacilli are inhaled with the air, but may also infect the lungs from the blood carrying them from tuberculosis in other parts of the body. The bacilli are incapable of independent movement. This difficulty is too readily overcome in the body, as the streams of blood and lymph easily carry them along.

Their movements in the body may be aided by certain scavengers that are crawling about in our tissues and circulating in our blood; namely, the wandering cells of connective tissue and the white blood corpuscles. These take up the bacilli by wrapping their substance around them; then, for a time, they crawl about carrying with them the bacilli. In this attempt to devour the tubercle bacillus, they often find they have caught a Tartar, who in turn feeds and multiplies in them, and thus their wandering days soon end.

Many other diseases are known to be caused by bacteria, such as anthrax, cholera, pneumonia, typhoid fever, erysipelas, leprosy, suppuration, and ordinary blood-poisoning. Before Sir Joseph Lister introduced the system of antiseptic surgery, bacteria were a most fertile source of danger in surgical operations by the decomposition and suppuration they set up in the wounds.

In this short paper it is impossible to describe the characteristics of any other pathogenic bacteria, but perhaps enough has been written to show the great danger to which we are exposed from attacks by an immense army of minute foes.

FOREST FORMATIONS
--M. J. SCHLEIDEN