Chapter X: Cryptogams (1)

I. THEIR PLACE IN NATURE

=331. Order of development.=—All the forms that have hitherto claimed our attention belong to the great division of Spermatophytes, or seed-bearing plants, designated also as _Phanerogams_, or flowering plants. They comprise the higher forms of vegetable life, and because they are more conspicuous and better known than the other groups, they have been taken up first, since it is more convenient, for ordinary purposes, to work our way backward from the familiar to the less known, rather than in the reverse order.

But it must be understood that this is not the order of nature. The geological record shows that the simplest forms of life were the first to appear, and from these all the higher forms were gradually evolved. There is no sharp line of division between any of the orders and groups of plants, but the line of development can be traced through a succession of almost imperceptible changes from the lowest forms to the highest, and it is only by a study of the former that botanists have come to understand the true nature and structure of the latter.

=332. Basis of distinction.=—_Cryptogams_, or seedless plants as a whole, are distinguished from the phanerogams by their simpler structure and by their mode of propagation, which in the former is by means of spores, while in the phanerogams it is by seeds. A spore is a simple organic body, consisting usually of a single cell which separates from the parent plant at maturity and gives rise to a new individual. A seed is a complicated, many-celled structure, containing within itself the rudimentary structure of a new plant already organized.

Beginning with the simplest forms, cryptogams are grouped in three great orders:—

=333. I. Thallophytes=, or thallus plants.—This group takes its name from the _thallus_ structure that characterizes its vegetation. In its typical form, a thallus is a more or less flat, expanded body, of which the lichens and liverworts offer familiar examples among land plants, and the kelps and laminarias among seaweeds. It may be of any size and shape, however, and sometimes consists of a mere filament, as in the common brook silk, or even of a single cell (Fig. 429). The term is applied in general to the simplest kinds of vegetable structure, in which there is no differentiation of tissues, and no true distinction of root, stem, and leaves. While it is not peculiar to the thallophytes, it has attained its most typical development among them, and the name is therefore retained as distinctive of that group. It embraces two great divisions, the Algæ and Fungi. The first includes seaweeds and the common freshwater brook silks and pond scums, besides numerous microscopic forms whose presence escapes the eye altogether, or is made known only by the discolorations and other changes caused by them in the water. To the fungi belong the mushrooms and puffballs, the molds, rusts, mildews, and the vast tribe of microscopic organisms called _bacteria_, which are so active in the production of fermentation, putrefaction, and disease.

=334. II. Bryophytes=, or moss plants.—This group likewise contains two main divisions, Mosses and Liverworts. Familiar examples of the latter are the flat, spreading green plants, bearing somewhat the aspect of lichens, met with everywhere on wet rocks and banks around shady watercourses. The name is a reminiscence of their former use in medicine as a specific for diseases of the liver, and not, as in the case of the liver leaf, of a fancied resemblance to that organ.

Mosses are one of the best defined of botanical orders, and are easily recognized by their slender, leafy fruiting stalks, growing usually in dense, spreading mats, and presenting every appearance of a highly organized structure, well differentiated into root, stem, and leaves.

The liverworts represent the more primitive division of the group, and in some of their forms approach so near the thallophytes that it is not difficult to recognize them as connecting links in the same chain of life. Their relationship to the next higher group is not clear, but while they represent a more primitive stage of evolution than the mosses, the development of the latter has followed a course divergent from the main line of evolutionary progress.

=335. III. Pteridophytes=, or fern plants, are classed roughly in the three divisions of ferns, horsetails, and club mosses. They differ greatly in structure, but all possess a vascular system, and a well-organized structure of root, stem, and leaves. They rank next to the spermatophytes in the order of development, and the group is of especial interest on account of its relationship to the higher plants. One of its divisions, the club mosses, has probably given rise to at least one section of the gymnosperms, while the ferns are regarded as the ancestors of the true flowering plants, which make up the great class of angiosperms, and represent the highest type of evolution yet attained in the vegetable kingdom.

II. THE ALGÆ

MATERIAL.—Simple forms of green algæ can be found on the shady side
of tree trunks, damp walls, old fence palings, and the outside of
flowerpots. _Pleurococcus_, one of the commonest kinds, occurs as a
green, powdery mat or felt in damp places, and is often accompanied
by _protococcus_, another good specimen for study. _Spirogyra_ and
other filamentous algæ can be found in stagnant pools and ditches
and in old rain barrels.

APPLIANCES.—Eosin solution, nitric acid, alcohol, iodine solution;
a white china plate; a hand lens; a compound microscope, and slides.

=336. Variety of forms.=—This group embraces plants of the greatest diversity of form and structure, from the minute volvox and desmids that hover near the uncertain boundaries dividing the vegetable from the animal world, to the giant kelps of the ocean, which sometimes attain a length of from six hundred to one thousand feet. They are usually classed according to their color, as green, brown, and red algæ, including various subdivisions of each group. They all contain chlorophyll, by means of which they manufacture their own food, though in the red and brown divisions it is masked by the presence of other pigments—an adaptation to the modified light that reaches them at various depths under water. With few exceptions they can live only in the water, and unlike any other form of plant life, attain their highest development in the salty depths of the ocean. The freshwater forms are small and inconspicuous, and generally of a more simple type than the seaweeds. The great majority of them belong to the two classes of green and blue-green algæ. The former is believed to have furnished the type from which the higher plants have been evolved.

=337. Study of a one-celled alga.=—Put a little of the green algæ in water on a glass slide. Hold up to the light, or over a sheet of white paper, and examine with a hand lens; then place under the microscope. It will probably be found to contain a number of minute organisms, but the pleurococci can be recognized as small round bodies of a bright green color, some of them separate, others adhering together in groups of two, four, or more, with the sides that are in contact slightly flattened. Each of these bodies is an individual plant consisting of a single cell, whence they are said to be _unicellular_. Draw one of the single cells and one of the groups, or colonies, as they appear under the microscope. Try to make out the cell wall and the nucleus, and label all the parts (see 7). If you have any difficulty in distinguishing the cell wall, drop a little glycerine or salt water on the slide. This will cause the cell contents to shrink by osmosis (56, 59). Can you make out the structure of the cell colonies? They have resulted from the peculiar mode of multiplication that prevails among this class of plants. A cell elongates, contracts in the middle, and divides into two parts, each of which becomes an independent plant like the mother cell. See if you can find one in the process of division. The daughter cells repeat the process, each one giving rise to two new individuals, and so on indefinitely. The new cells do not always separate immediately on their formation, but frequently adhere together for a time, in colonies, before falling away and beginning an independent existence.

=338. Reproduction by fission.=—This kind of reproduction is called _fission_, or cell division, and marks a very primitive stage of development. Under stress of adverse conditions the cells formed by division may remain inactive for a time. They are then called _resting spores_, and when more favorable circumstances arise, they begin again their work of reproduction and growth as actively as ever.

=339. Meaning of the name.=—The suffix _coccus_ is a Latin noun (plural _cocci_) meaning a grain or berry, and is a general term applied to any small, round organism consisting of a single cell; hence, _micrococcus_, a minute round body; _protococcus_, a primitive form, or prototype of one-celled bodies; and _pleurococcus_, which may be freely translated “a one-sided little round body,” from the flattening of the adjacent sides during fission—_pleuro_ meaning lateral, or pertaining to the side.

It is important to remember this definition, as the term _coccus_ is of very frequent occurrence in works of biology, as a suffix for designating small round bodies of various kinds.

=340. Examination of a filamentous alga.=—Place on a white dish a few drops of water containing some of the green pond scum common in stagnant pools and ditches. Examine with a hand lens; of what does it appear to consist? Are the filaments all alike, or are they of different lengths and thickness? Soak a number of them in alcohol for half an hour and examine again; where has the green matter gone? Do these algæ contain chlorophyll? (336; Exp. 65.) This class are called filamentous algæ on account of their slender, threadlike thalli, which look like bits of fine floss floating about in the water. The bubbles of oxygen which they sometimes give off in great abundance cause the frothy appearance that has given rise to their popular name, “frog spit.”

=341. Spirogyra.=—The filamentous algæ are very numerous, and a drop of pond scum will probably contain several kinds. At least one of these, it is likely, will be a _Spirogyra_, as this is one of the commonest and most widely distributed of them all. Place a filament under the microscope and notice the spiral bands in which the chlorophyll is disposed within the cells. It is from this spiral arrangement that the species takes its name. Do you notice any roundish particles inclosed in the chlorophyll bands? Test with a little iodine solution and see what they contain. Each filament will be seen, when sufficiently magnified, to consist of a number of more or less cylindrical cells joined together in a vertical row, and thus forming the simple threadlike thallus which characterizes this class of algæ. Physiologically, each cell is an independent individual, and often exists as such. Can you see the cell nucleus? If not, place a few filaments in a solution of eosin and add a drop of acetic acid to give the solution a pale rose color. After twenty to thirty minutes, examine again; the nucleus will be stained a deep red. If you can find an unbroken filament, examine both ends to see whether there is any differentiation of base and apex.

=342. Conjugation.=—See if you can find two filaments sending out lateral protuberances toward each other. Watch and notice that after a time these projections come together and unite by breaking down the cell walls dividing them, the protoplasm in each contracts, the contents of one pass over into the other, and the two coalesce, forming a new cell but little, if any, larger than the original conjugating bodies. This cell germinates under favorable conditions and produces a new individual. This method of reproduction is known as _conjugation_. The cells thus produced by the union of the contents of two separate cells may either germinate at once, and give rise to new individuals, or remain quiescent for a time, as resting spores.

Practical Questions

1. Are any of the green algæ parasitic? How do you know? (186, 336.)

2. Why is their presence in water regarded as denoting unhygienic
conditions?

3. Mention some of the ways in which their presence may contribute
to the contamination of drinking water.

4. Refer to Exp. 66, and account for the bubbles and froth that
usually accompany these plants in the water.

5. Can you suggest any other causes than the evolution of oxygen
that might produce the same effect?

6. Is the presence of these gas bubbles of any use to floating
plants?

III. FUNGI

=343. Classification.=—In the fungi the thallus structure is greatly modified, appearing usually as a network of fine threads called the _mycelium_ (pl., _mycelia_), from a Greek word meaning “fungus” (369). These plants are all, with a few doubtful exceptions, parasites or saprophytes which contain no chlorophyll and are incapable of supporting an independent existence. Biologists are divided as to their position in the genealogical tree of life. The weight of authority at present inclines to the view that they are degenerate forms derived from the algæ, but they have been so modified by their parasitic habits as to render their position in the general scheme of life a doubtful one. They represent an offshoot, or side branch, as it were, of the great evolutionary line, and so may be considered for the present as standing apart in a class by themselves.

=344. Numbers and variety.=—Fungi exceed every other class of living organisms both in the number of species and of individuals composing them. They include such diverse forms as bacteria, molds, rusts, mildews, mushrooms, and the like, ranging in size all the way from the giant puffball, a foot or more in diameter, to the almost inconceivably minute influenza bacillus, of which nearly two thousand million can inhabit a single drop of water without inconvenient crowding!

=345. The parasitic habit.=—But while their life history is obscure and hard to trace, the fungi are, as a class, well differentiated by their parasitic habit. They contain no chlorophyll, can manufacture no food, and consequently have to obtain it ready-made from the tissues of living or dead animals and plants. On this account they are active agents in the production of disease and decay, especially certain of those manifold forms that have been grouped together under the general head of bacteria. While not responsible for all the disease known to be caused by living organisms,—some very serious ones, such as malaria and cattle fever, being due to animal parasites,—the majority of those that have been most carefully investigated are traced to the bacteria, or other fungi. After any of these parasites have found a lodgment in the body of an organism whose tissues furnish them a congenial habitat, they multiply with enormous rapidity, and through the action of certain poisons called _toxins_, which they excrete, give rise to the most destructive diseases in both animals and plants; and no rational sanitary science is possible without a knowledge of their habits and life history. Add to the vast amount of human suffering that is to be laid at their door the economic damage done by rust and smut fungi, by molds and blights and mildews, and we shall be tempted to conclude that the “battle of life” is largely a struggle against these invisible foes.

=346. Useful fungi.=—Not all fungi, however, are injurious. On the contrary, the great majority of them are harmless, and very many kinds are positively beneficial to man. Without the yeasts and bacteria of fermentation we could not have our bread and cheese. Other forms are active agents in the fertilization of soils, it having been estimated that there are 100,000 or more of these infinitesimal laborers at work in every cubic centimeter (about ¹⁄₁₆ of a cubic inch) of virgin soil! Even the bacteria of putrefaction, which we are accustomed to regard as the embodiment of all that is foul and loathesome, are engaged in an unceasing work as scavengers, without which life would no longer be possible on our globe, as will be shown in the following section.

A. BACTERIA

MATERIAL.—A vessel of water in which hay has been left to soak for
several hours; a freshly boiled potato.

APPLIANCES.—A double boiler for sterilizing; a number of clean
glass jars and bottles; cotton wool for stoppers; a compound
microscope.

CULTURE MEDIUMS.—A freshly boiled potato answers very well for
ordinary purposes. “Bread mash” can be made by drying some bread
crumbs in an oven, then mashing and mixing them to a paste with
boiling water; sterilize by three successive heatings in a double
boiler. A sterilized preparation of gelatine solution is the medium
most commonly used.

=347. How to obtain specimens for observation.=—While bacteria are plentiful almost everywhere, it is not always easy to capture them just when and where you want them. For this purpose, put some hay in water and leave in a warm place away from the light until the liquid becomes cloudy or a film forms on the surface. This will show that bacteria are present. If it is desired to study any particular kind of bacterium, inoculate one of the culture mediums described under “material,” or a few drops of sterilized extract of beef, with a small quantity of the substance to be examined, or with dust or scrapings from the locality under consideration.

EXPERIMENT 93. BY WHAT MEANS ARE BACTERIA COMMONLY DISTRIBUTED?—Put
a slice of freshly boiled potato into each of three glass tumblers
and cover with a filter of cotton wool held in place by tying
tightly with a cord, or by an elastic band. Set them all in a
vessel of water, bring it to a boil, and keep at that temperature
for half an hour, to sterilize the air in the tumblers. When they
have cooled, lift the cotton from (1) for a minute or two and then
replace. Carefully pass the tip of a medicine dropper through the
filter of (2) so as to prevent the entrance of unsterilized air,
and put on the slice of potato a small quantity of the bacterial
liquid prepared as directed in the last paragraph. Leave (3)
unopened. Keep all together in a warm, dark place and observe at
intervals of from 12 to 24 hours. Do any bacteria appear in (3)?
Do any appear on the potato in (2), where the liquid was dropped?
Are they more, or less abundant than in (1)? Since cotton wool is
entirely impervious to the smallest microörganisms known, would you
judge from this experiment that bacteria can get into any place
unless carried there by the air, or by some other means?

EXPERIMENT 94. CAN BACTERIA BE CARRIED BY PURE AIR?—On a warm (and
preferably cloudy) day, put a slice of potato on a plate, and leave
uncovered in an unused room or closet, free from dust, and kept
carefully closed. Put another slice arranged in exactly the same
way in an open window on a dusty street, or in a room that is used
and daily swept and dusted. Do bacteria appear in the first plate?
In the second? Is air free from dust a good conveyor of bacteria?

EXPERIMENT 95. WHAT CONDITIONS ARE FAVORABLE TO BACTERIAL
GROWTH?—Strain some of your culture liquid into half a dozen small
bottles of the same size, filling each about half full. Put (1) in
a dark, cool place—on ice, if the weather is warm; (2) in a dark,
warm place; (3) in a warm, well-lighted place; into (4) put a drop
of carbolic acid, formalin, corrosive sublimate, or boracic acid,
and keep in a dark, warm place. Keep (5) in boiling water for half
an hour or more, and then place beside (2). Keep (6) in a freezing
mixture of salt and ice for several hours, then place with (2) and
(5). Examine all at intervals of from 12 to 24 hours. In which
bottles is the presence of bacteria indicated by cloudiness of the
contained liquid, or the formation of a surface film? In which do
they appear first? In which most abundantly? In which last, or not
at all? What is the effect of light and darkness on their growth?
Of heat and cold? Of disinfectants? Name the circumstances that
tend to hinder their growth, in the order of their efficacy.

=348. Microscopic study of bacteria.=—Put a drop of hay infusion on a slide and examine with the highest power of the microscope. You will see a multitude of very small glistening bodies including different kinds of bacteria, a majority of which are probably the hay bacillus, _B. subtilis_, shown in Figs. 443, 444. Notice that some forms move about freely, while others are non-motile. Which kind are the more numerous? The motion may be either mechanical, resembling that of the small dust particles we see dancing about in the sunshine, or apparently voluntary, and caused by the vibration of little whiplike cilia. Can you distinguish the two kinds? Try to make out clearly the different shapes you see. Some appear as slender chains or filaments, but this is due to the individual cells’ adhering together for a time before breaking up and beginning an independent existence. The small, rounded bodies, like a period (Fig. 438), are _cocci_; the slender, rod-shaped ones—sometimes slightly curved (Fig. 440)—are _bacilli_ (sing., _bacillus_); the comma-shaped ones, and those generally showing a slight spiral curvature, are _vibrios_ (Fig. 441); the spirally twisted ones, like a corkscrew (Fig. 442), are _spirilli_ (sing., _spirillum_). These are the principal forms which it is important to distinguish and remember. The names are applied very loosely, however, in practice, bacillus being often used as a general term applicable to almost any kind,—the spirillum of cholera, for instance, being commonly known as the cholera bacillus, while by some authors vibrios are ranked as a variety of spirillum.

=349. Life history of a typical bacterium.=—A pure culture of the _Bacillus subtilis_ can easily be obtained by boiling some of the hay infusion for half an hour and then leaving in a warm place till the usual indications of the presence of bacteria appear (347). The spores of this micro-organism are so resistant that they can withstand the temperature of boiling water for several hours, while those of most other forms of bacteria are killed by a few minutes’ exposure to it; hence, the crop that develops after boiling will consist of a pure culture of the hay bacillus.

In their active state these organisms will be seen to consist of single-celled, rod-shaped bodies, about three or four times as long as broad, and generally cohering in bands or filaments, as shown in Fig. 444, _c_. The black dots within the cells are the spores. Each individual bacterium produces but a single spore, or rather becomes a spore itself, by the contraction of its contents and the formation around them of a strong inclosing membrane. On germinating, the spores give rise to little ciliated, one-celled organisms called “swarm spores,” that swim about freely in the containing medium and multiply rapidly for a time by cell division. After this they pass again into the quiescent state, ready, whenever favorable conditions arise, to begin anew the repetition of their life cycle, which is an irregular alternation of cell division and spore formation.

=350. Resistance of spores.=—Bacteriologists are not fully agreed as to the cause of spore formation, some holding that it takes place only when conditions are most favorable for bacterial growth, others claiming the reverse. The consensus of opinion at present is toward the view that the spores are a provision for tiding over periods of stress and difficulty. They are capable of retaining their vitality for a long time, and are much harder to kill than the bacterial cells in their ordinary vegetative state, as was seen in the case of the hay bacillus. The spores of one species of potato bacillus have retained their vitality after four hours of boiling, and those of the typhoid bacillus after continuous exposure to a freezing temperature for more than three months. The majority of bacteria, in their vegetative state, are, however, either killed or rendered inert by temperatures ranging below 10° or above 50° centigrade—equivalent to about 50° and 122° Fahrenheit, respectively. It is easy to see what important bearing these facts have on the process of disinfection.

=351. Reproduction and multiplication.=—The ordinary mode of reproduction in bacteria, as in other unicellular organisms, is by fission (337, 338). As each individual forms but a single spore, no increase in numbers could take place by this means alone. Hence, while the spores are an important factor in the preservation of the species by continuing its existence under conditions which the active organisms could not survive, their successful propagation depends on their power of rapid multiplication by division. If this process were to go on unchecked, every hour, in an unbroken geometrical progression, the progeny of a single bacterium would, in 24 hours, number nearly 17 million; in 25 hours, 34 million; in 26 hours, 68 million, and in five days they would cover the entire surface of the globe, land and sea, to a depth of 3 feet! In ordinary standard milk sold by dairymen, and containing, when examined, less than 10,000 microbes to the cubic centimeter,—about 20 drops,—the number was found to have increased after 24 hours to 600 million. It is comforting to know, however, that the majority of these are of the harmless kinds which are the active agents in the making of buttermilk and cheese.

The effects of their rapid multiplication will be better appreciated when we consider that bacteria are the smallest of known living creatures. If 1000 of the influenza bacilli were spread out in a single layer with their sides touching, but not overlapping, they would not take up more room than one of the periods used in punctuating this book; and a coccus concerned in a tubercular disease prevalent among cattle in South America has recently been discovered, of which double that number could be accommodated in the same space.

=352. Distribution of bacteria.=—Ordinary air, when free from dust, contains, on the average, not more than five germs to the liter—equal to about 1 for every 12 cubic inches. Pathogenic, or disease-producing, germs seldom occur in ordinary fresh air, and even when present are, under ordinary circumstances, harmful only to people whose bodies, by reason of physical weakness or unhygienic habits, offer a congenial soil for their multiplication. Numerous instances are known in which perfectly healthy persons have carried about infectious disease germs in their bodies and even transmitted them to others without experiencing any inconvenience, or even being aware of their presence. Among others, the germs of pneumonia, diphtheria, and tuberculosis are often found in the mouth, nose, and sputum of perfectly healthy persons. There are also a number of bacteria that are regular inhabitants of the mouth, some of which are the cause of decayed teeth and foul breath. One form of bacterium, concerned in the production of inflammation and abscesses (_Staphylococcus_) is so constantly present on the human epidermis that one authority has declared it impossible to sterilize the skin so thoroughly as to free it entirely of this microbe. It is ordinarily not harmful unless it comes in contact with open wounds and abrasions.

=353. The economic importance of bacteria.=—It is hard to say whether these organisms concern us most on account of the damages attributable to them on the one hand, or the benefits we owe them on the other. If they were all as harmful as the pathogenic kinds, life would hardly be possible on the globe, while without their presence life as we know it would have ceased to be possible long ago. They are nature’s great army of scavengers, the sole agents of decomposition, without which dead organic matter would be subject only to the slow changes by which the rocks and mineral matter of the earth’s crust are disintegrated, and the undecomposed bodies of the vast procession of plants and animals that have existed since life first began on our globe would long ago have cumbered its surface to such an extent as to render impossible the continued development of life such as we know.

=354. Sterilization= is the process of ridding a substance of living microörganisms. To do this effectively, the process must be repeated several times at intervals, so as to give any spores that may have survived previous applications time to pass into the vegetative state, when their power of resistance is diminished and they are more easily destroyed. The incubation period, as the time required for the germination of the spores is called, is different for different kinds of bacteria; hence the importance, from a sanitary point of view, of a thorough knowledge of their life history.

=355. Disinfection= is sterilization on a large scale, and the same principles apply to both. Heat is the safest disinfectant for objects that will bear it, if continued long enough and repeated often enough at a sufficiently high temperature. Freezing will destroy some kinds of germs and check or retard the development of nearly all, but is not to be relied on as a permanent germicide, since even among flowering plants there are many kinds, not only of seeds, but of perennial vegetative forms that are capable of enduring an arctic temperature of many degrees below freezing for long continued periods.

Chemical disinfectants act usually as microbe poisons, and are unsuitable as sterilizers for food, though valuable in the purification of houses, clothing, and utensils—especially the instruments employed in surgical operations.

The prevention of the growth of bacteria, especially in wounds and surgical incisions, whether by means of chemical or physical agencies, is known as _antisepsis_.

Practical Questions

1. Why should a person recovering from an ague continue for some
time after to take quinine every third or every seventh day? (350,
354.)

2. Name some of the principal diseases produced by bacteria.

3. What is the principle to be acted on in the avoidance of such
diseases? (Exps. 94, 95.)

4. Are the same means equally effective for prevention and for
cure? (354, 355; Exps. 93-95.)

5. Why is “fresh air” beneficial in a sick room? (352; Exp. 94.)

6. Does it act as a disinfectant, or as a mere diluent of the
infected air of the room? (352.)

7. Why ought preserved fruits and vegetables to be scalding hot
when put into the can? (355.)

8. Why is it necessary to exclude the air from them? (Exps. 93, 94.)

9. Reconcile question 8 with question 5.

10. Why does the use, for drinking purposes, of water that has been
boiled render a person less liable to infectious diseases? (355.)

11. Was the old-fashioned practice of handing the baby round to be
promiscuously kissed by friends and neighbors a good one for the
baby? (352.)

12. Why is the spitting habit to be condemned? The use of common
drinking cups in schoolrooms and other public places? (352.)

13. Is it proper from a sanitary point of view that roommates at
a boarding school, or even members of the same family, should use
soap, towels, and other articles of the toilet in common? (352.)

B. YEASTS

MATERIAL.—A piece of fresh baker’s yeast, some warm water, and a
little honey or sugar solution; a pipette, or a medicine dropper;
three or four clean pint bottles or preserve jars.

To raise a crop of yeast fungi for observation, rub one fourth of a
fresh yeast cake in water enough to make a paste; add one pint of
water, with a tablespoonful of honey or sugar, and stir well.

EXPERIMENT 96. WHAT CONDITIONS FAVOR THE GROWTH OF YEAST?—Pour
equal parts of the liquid made as directed (see Material) into each
of three pint bottles, stopper lightly, and label. Put (1) in a
warm, dark place; (2) in a cool, dark place; and (3) in a bright
light in a warm place. Observe at intervals of a few hours the
changes that occur in each. Notice the bubbles that rise from the
liquid. In which bottle do they form most rapidly? Lower a lighted
match into it, or transfer some of the gas with a pipette into a
vessel containing limewater, and tell what it is. Taste some of the
fermenting liquid. Is it sweet? What has become of the sugar that
was put into it?

=356. Yeasts and ferments.=—Yeasts belong to a very different order of fungi from the bacteria, but on account of their simplicity of structure and the similarity of their action to that of some of the latter, it is usual to consider them together. They are the active agents of fermentation, and include a large number of species. The kind used for household purposes is the same as that employed in making beer. Of this species there are many varieties, each one of which gives a characteristic taste to the beer made from it; and brewers, by paying attention to the cultivation of yeasts, give their product the special flavors peculiar to the different brands. This kind of yeast is not known to exist except in a state of cultivation, and probably owes its survival and present condition of development to a symbiosis with man, on account of its usefulness in bread making, and still more, perhaps, to its part in the gratification of his bibulous propensities, for among savage tribes the manufacture of fermented liquors is practiced long before the wholesome art of bread making.

There are other yeasts existing in a state of nature, such as those on the surface of fruits, which cause the latter, under certain circumstances, to ferment and decay. For this reason artificial ferments are not needed in making wine and other alcoholic liquors from fruits. Fermentation is also caused by certain forms of bacteria, as in the formation of vinegar and the souring of milk. Such bacteria often contaminate the yeast ferments.

=357. Microscopic examination.=—Place a drop of the cultural liquid on a slide and examine under the highest power of the microscope. What do you see? These egg-shaped bodies are yeast plants, unicellular organisms like the pleurococcus. Do you see any chlorophyll? Are the yeasts parasitic? How do you know? What do they live on? (Suggestion: What food substance that has disappeared was put into the culture liquid?) In getting their nourishment from the sugar, these fungi disintegrate it into alcohol and carbon dioxide, which is a process of fermentation. It is the bubbles of gas that were seen rising in the liquid which cause beer to effervesce and bread to rise. They permeate the dough and by their expansion produce the sponginess peculiar to leavened bread. Look for a cell with a bud forming on it; from what part does it appear to grow? Where a number of buds remain for some time attached to the mother cell (Fig. 449), they form a _colony_. Make a sketch of a single cell and of a colony of two or more adherent ones, labeling all the parts. If the cell wall cannot be made out clearly, run a little glycerine, or salt water, under the cover glass with a medicine dropper. What causes the contents of the cell to contract and leave the wall? (56, 59.)

=358. Reproduction.=—From time to time buds break away from the mother cell and form new individuals or colonies of their own. This process is called multiplication by budding, and is only another form of cell division.

Whenever reproduction takes place by other means than seeds or spores, it is said to be _vegetative_. This sort of reproduction is not confined to unicellular plants, but exists also among the phanerogams, the propagation of species by means of buds, tubers, rootstocks, runners, grafting, and the like being variations of the same process. On the other hand, yeasts and bacteria and the unicellular algæ have the power, under extreme conditions, to form resting spores, which sometimes lie dormant for years and resume their activity when favorable conditions return.

Practical Questions

1. When is fermentation useful to man?

2. What is the effect on canned fruits and vegetables if yeast
cells get into them?

3. Why does milk turn sour in warm weather? (350, 351; Exp. 96.)

4. Why do buttermilk and clabber spoil if left standing too long?
(345, 356.)

5. What causes bread to be “heavy”? (356, 357.)

6. Why will dough not rise unless kept in a warm place? (Exp. 96.)

7. Why is beer kept cold during fermentation? (350, 356.)

C. RUSTS

MATERIAL.—A leaf of wheat affected with red rust; a leaf or a stalk
with black rust. Some barberry leaves with yellowish pustules on
the under side, which under the lens look like clusters of minute
white corollas. These are popularly known as “cluster cups.” As the
spots on barberry occur in spring, the red rust in summer, and the
black rust in autumn, gather the specimens as they can be found,
and preserve for use.

The orange leaf, or brown, rust (_Puccinia rubigo-vera_) is more
common in some parts of the country than the ordinary wheat rust
(_Puccinia graminis_), but the two are so much alike that the
directions given will do for either. If the orange leaf-rust (so
named from its color, and not from any connection with orange
leaves, the logical relation of the words being orange leaf-rust,
and not orange-leaf rust) is used, the cups and pustules should be
looked for on plants of the borage family—comfrey, hound’s-tongue,
etc. The orange leaf-rust of apple is caused by a fungus which will
serve to illustrate the same class of parasites. The “teleuto”
stage of this will be found on cedar trees, in the excrescences
commonly known as “cedar apples”; the “cluster cups” on the leaves
of apple and haw trees affected with the disease.

=359. Red rust.=—Uredo stage. Examine a leaf of “red rusted” wheat under the lens, and notice the little oblong brown dots that cover it. These are clusters of spore cases, and are the only part that appears above the surface. Viewed under the microscope, the red rust will be seen to consist of a mycelium (see Fig. 452), which ramifies through the tissues of the leaf and bears clusters of single-celled reddish spores that break through the epidermis and form the reddish brown spots and streaks from which the disease takes its name. These spores, falling upon other leaves, germinate in a few hours and form new mycelia, from which, in six to ten days, fresh spores arise. Formerly this was thought to complete the life history of the fungus, to which the name of _Uredo_ was given. It is now known, however, that the red rust is merely a stage in the life cycle of the plant, and to this stage the old name uredo is applied, the spores being called _uredospores_.

=360. Black rust.=—Teleuto stage. Next examine with a lens a part of the plant attacked by black rust. Do you observe any difference except in the color? Do the two kinds of rust attack all parts of the plant equally? If not, what part does each seem to affect more particularly? At what season does the black rust appear most abundantly? Place a section of the diseased part under the microscope and notice that the difference in color is due to a preponderance of long, two-celled bodies with very thick, black walls (Fig. 453). These are called _teleutospores_, a word meaning “final spores,” because they are formed only toward the end of the season. They are developed from the same mycelium with the uredospores, and are not a product of the latter, but collateral with them and belong to the same stage in the life history of the fungus. After they appear, the uredospores cease to be developed at all, and only the dark teleutospores are produced. These remain on the culms in the stubble fields over winter, ready to begin the work of reproduction in spring. For this reason the teleutos are popularly known as “winter spores” in contradistinction to the uredos, or “summer spores,” whose activity is confined to the warm months.

It was formerly supposed that black rust was caused by a different fungus from that producing red rust, and to it the name _Puccinia_ was given. This has been retained as a general designation for all fungi undergoing these two phases, and the particular form of fungus that we are now considering is known in all its stages as _Puccinia graminis_.

=361. The nonparasitic stage.=—The formation of teleutospores completes that portion of the life history of the fungus during which it is parasitic on wheat and grasses of different kinds. In spring they begin to germinate on the ground, each cell producing a small filament, from which arise in turn several small branches. Upon the tip of each of these branches is developed a tiny sporelike body called a _sporidium_ (Fig. 454), which continues the generation of the rust fungus through the next stage of its existence. The filament which bears these sporidia is not parasitic, but when the sporidia ripen and the spores contained in them are scattered by the wind, there begins a second parasitic phase, which forms the most curious part of this strange life history.

=362. The æcidium.=—Examine next the under side of some barberry leaves (or comfrey, etc., if orange leaf-rust is used) for clusters of small whitish bodies that appear under the lens like little white corollas with yellow anthers in the center. Examine a section of one of these under the microscope and notice that the yellow substance is composed of regular layers of colored spores. The corolla-like receptacles containing them, popularly known as “cluster cups,” are borne on a mycelium produced from the spores described in the last paragraph. This mycelium is parasitic on barberry or other leaves, according to the kind of fungus, and was long believed to be a distinct plant, to which the name _Æcidium_ (pl., _Æcidia_) was given. This term is now applied to the cluster cups, and those fungi which at any period of their life history produce them are called æcidium fungi.

=363. Spermogonia.=—On the upper surface of the leaves that bear the æcidia, notice some small black dots hardly larger than pin points, but which, when sufficiently magnified, appear as little flask-shaped bodies (Fig. 455) under the epidermis. These are known as _spermogonia_, or _pycnidia_. When mature, they break through the epidermis so that the necks protrude, and discharge a quantity of minute cells or spores, very like some that, later on, we shall find playing an important part in the reproductive processes of certain other fungi, and of mosses and liverworts. In the rust fungi, however, their function is not understood. They may possibly be survivals of organs which were once active in the life processes of the plant, but have become useless under changed conditions. Do such organs throw any light on the evolutionary history of plants?

=364. Connection between barberry and wheat rust.=—With the discharge of the æcidium spores, the part of the life cycle of the fungus spent on the barberry comes to an end, and it is ready to begin the uredo-teleuto stage over again as soon as it finds a suitable host. Where there are no barberries, it is capable of propagating without them, either by adapting itself to some other host plant, or by omitting the æcidium stage altogether. The parasitic habit being an acquired one, the fungus, like some animal organisms that we know of, can often be “educated” by force of circumstances into tolerating, and even thriving upon, foods which under other circumstances it would reject. The wheat rust is known to be capable of propagating year after year in the uredo stage, the spores surviving through the winter on volunteer grains and grasses; and in no other country in the world does rust do greater damage to the wheat crop than in Australia, where the barberry is practically unknown. This power of accommodation possessed by many parasites is one of the difficulties the agriculturist has to contend with in the development of rustproof varieties.

=365. Polymorphism.=—Plants that pass through different stages in their life history are said to be _polymorphic_, that is, of many forms. The habit is very common among the lower forms of vegetation. The fact that one or more of the phases are sometimes omitted, as the æcidium phase of wheat rust in warm climates, suggests the idea that it may be of use in helping the plant to tide over difficult conditions. Besides giving better chances of obtaining nourishment, it probably has the same effect as cross fertilization among flowering plants, in imparting increased strength and vitality to the succeeding generation. Wheat rust produced from barberry æcidia is said to be much more vigorous—and consequently more destructive—than when derived from a uredo that has reproduced itself for several generations.

=366. The damage done by rust= to the host is through the destruction of its tissues by the mycelium. The chlorophyll is destroyed so that the plant can no longer manufacture food, and is too starved to produce good grain. There are many varieties of wheat rust, which have been found on twenty-seven different kinds of grain. Most of them are specialized to a particular host plant and will not, ordinarily (364), infest any other. Has this fact any bearing upon the production of rustproof varieties?

Practical Questions

1. Is a farmer wise to leave scabby and mildewed weeds and bushes
in the neighborhood of his grain fields? (364, 365.)

2. Are there any objections to the presence of volunteer grain
stalks along roadsides and in fence corners during winter? (364.)

3. Should cedar trees be allowed to grow near an apple orchard?
Give a reason for your answer. (p. 317, Material.)

4. Should diseased plants be plowed under? (361.)

5. What disposition should be made of them?

6. Ought diseased fruits to be left hanging on the tree?

7. Why is it necessary to pick over and discard from a crate or bin
all decaying fruits and vegetables?

8. Does a rotation of crops tend to prevent the spread of disease
in plants? Give reasons for your answer.

9. Are rustproof varieties to be relied on indefinitely? (364.)

D. MUSHROOMS

MATERIAL.—Any kind of gilled mushroom in different stages of
development, with a portion of the substratum on which it grows,
containing some of the so-called spawn. The common mushroom sold in
the markets (_Agaricus campestris_) can usually be obtained without
difficulty. Full directions for cultivating this fungus are given
in Bulletin 53 of the U. S. Department of Agriculture. From 6 to 12
hours before the lesson is to begin, cut the stem from the cap of a
mature specimen, close up to the gills, lay it, gills downward, on
a piece of clean paper, cover with a bowl or pan to keep the spores
from being blown about by the wind, and leave until a print (Fig.
466) has been formed.

=367. Mushrooms and toadstools.=—The popular distinction which limits the term “mushroom” to a single species, the _Agaricus campestris_, and classes all others as toadstools, has no sanction in botany. All mushrooms are toadstools and all toadstools are mushrooms, whether poisonous or edible. The real distinction is between mushrooms and puffballs, the former term being more properly applied to fungi which have the spore-bearing surface exposed.

=368. Examination of a typical specimen.=—The most highly specialized of the fungi, and the easiest to observe on account of their size and abundance, are the mushrooms that are such familiar objects after every summer shower. The _gilled_ kind—those with the rayed laminæ under the cap—are usually the most easily obtained. Specimens should be examined as soon after gathering as possible, since they decay very quickly.

=369. The mycelium.=—Examine some of the white fibrous substance usually called spawn through a lens. Notice that it is made up of fine white threads interlacing with each other, and often forming webby mats that ramify to a considerable distance through the substratum of rotten wood or other material upon which the fungus grows. This webby structure, often mistaken for root fibers, is the thallus or true vegetative body of the plant, the part rising above ground, and usually regarded as the mushroom, being only the fruit, or reproductive organ. Place some of the mycelium under the microscope and notice that it is composed of delicate filaments made up of single cells placed end to end, as in Spirogyra (341). These filaments are called _hyphæ_.

=370. The button.=—Look on the mycelium for one of the small round bodies called buttons (Fig. 457). These are the beginning of the fruiting body popularly known as the mushroom, and are of various sizes, some of the youngest being barely visible to the naked eye. After a time they begin to elongate and make their way out of the substratum.

=371. The veil and the volva.=—Make a vertical section through the center of one of the larger buttons after it is well above ground, and sketch. Notice whether it is entirely enveloped from root to cap in a covering membrane—the _volva_ (Fig. 458, _a_)—or whether the enveloping membrane extends only from the upper part of the stem to the margin of the cap—the _veil_ (Fig. 458, _d_); whether it has both veil and volva, or finally, whether it is naked, that is, devoid of both.

=372. The stipe, or stalk.=—Notice this as to length, thickness, color, and position; that is, whether it is inserted in the center of the cap or to one side (excentric), or on one edge (lateral). Observe the base, whether bulbous, tapering, or straight, and whether surrounded by a cup, or merely by concentric rings or ragged bits of membrane (the remains of the volva). Look for the _annulus_ or ring (remains of the veil) near the insertion of the stipe into the cap, and if there is one, notice whether it adheres to the stipe, or moves freely up and down (Fig. 459, _a_); whether it is thick and firm, or broad and membranous so that it hangs like a sort of curtain round the upper part of the stipe (Fig. 467, _a_). Break the stem and notice whether it is hollow or solid; observe also the texture, whether brittle, cartilaginous, fibrous, or fleshy.

=373. The pileus, or cap.=—Observe this as to color and surface, whether dry, or moist and sticky; smooth, or covered with scurf or scales left by the remains of the volva, as it was stretched and broken up by the expanding cap (Fig. 459, _p_, _p_). Note also the size and shape, whether conical, expanded, funnel-shaped (Fig. 460), or _umbonate_—having a protuberance at the apex (Fig. 459)—or whether the margin is turned up at the edge (revolute, Fig. 467), or under (involute, Fig. 459).

=374. The gills, or laminæ.=—Look at the under surface and notice whether the gills are broad or narrow, whether they extend straight from stem to margin, or are rounded at the ends, or curved, toothed, or lobed in any way. Notice their attachment to the stipe, whether _free_, not touching it at all; _adnate_, attached squarely to the stem at their anterior ends; or _decurrent_, running down on the stem for a greater or less distance (Fig. 460).

=375. The hymenium.=—Cut a tangential section through one side of the pileus and sketch the section of the gills as they appear under a lens, or a low power of the microscope. Notice that the blade consists of a central portion called the _trama_ (_tr_, Fig. 462) and a somewhat thickened portion, _h_, constituting the _hymenium_, or spore-bearing surface. Now examine, under a high power, a small section from the edge of a gill, including a bit of the trama. Notice that this last consists of a tissue of mycelial cells (Fig. 463) covered by the hymenium, or spore-bearing membrane, which is thickly clothed with a layer of elongated, club-shaped cells (_b_, _b_ and _p_, _p_, Fig. 463) set upon it at right angles to the surface. Some of these put out from two to four, or in some species as many as eight, little prongs, each bearing a spore (_s_, _s_, Fig. 463), while others remain sterile. The spore-bearing cells are called _basidia_; the sterile ones, _paraphyses_; and the whole spore-bearing surface together, the _hymenium_, from a Greek word meaning a membrane. It is from the presence of this expanded fruiting membrane that the class of mushrooms we are considering gets its botanical name, _Hymenomycetes_, membrane fungi. The hymenium is not always borne on gills, but is arranged in various ways which serve as a convenient basis for distinguishing the different orders. In the tube fungi, to which the edible boletus belongs (Figs. 464, 465), the basidia are placed along the inside of little tubes that line the under side of the pileus, giving it the appearance of a honeycomb. In another order, the porcupine fungi, they are arranged on the outside of projecting spines or teeth, while in the morelles they are held in little cups or basins.

=376. Spore prints.=—When the gills are ripe, they shed their spores in great abundance. Take up the pileus that was laid on paper, as directed under Material, on page 323, and examine the print made by the discharged spores; it will be found to give an exact representation of the under side of the pileus.