Chapter IX: Fruit

If we are shown a collection of delicious apples, pears, grapes, peaches and cherries, we form a very appreciative opinion of the use and function of fruit, but that opinion is somewhat modified when we are shown a basket of poppy-heads, acorns, the light downy seeds of the thistle, the small dry carpels of the buttercup or the winged fruits of the maple. We usually connect the term fruit with some luscious product of the vinery or kitchen-garden, and we may include as such the brightly-coloured berries of the hawthorn and wild rose, which are so conspicuous on trees and hedges in autumn; but if we examine the subject botanically we shall have to widen our ordinary conception of the term.

There is probably no part of a plant so difficult to understand as its fruit, and this difficulty is due to those many changes which I described in my last chapter. A very general definition of fruit is that it consists of the ripened ovary, and this will be found to be correct in a great number of cases, but this term is not exactly wide enough to express the general formation of all fruit. In some cases it is composed of the ripened ovary with the parts of the stalk or the original flower, enlarged or incorporated in the structure of the fruit, but in other specimens we find the ovary, although present, very little enlarged, and playing but a minor part in the ultimate character of the mature fruit.

No fact seems so emphatic to the observant botanist as that which upsets his artificial rules and classifications of plants and the parts of plants. We say, for instance, that fruit is the ripened ovary, and yet directly we leave our books and go out to study botany in the fields and woods, we find a large group of fruits perfectly innocent of any such structure. The firs and pines have no organ of this kind, and yet their fruits are most important and extremely interesting. Scarcely any part of a plant varies so much in different species as the fruit does. Although leaves may be found of every size and shape, they still have some general similarity of form, but we hasten to observe what an immense contrast there is between the huge _Musa_ fruit (banana) and that of the oak (acorn), although the former is, compared to the latter, but a poor weakly plant.

Again, let us note the difference between the cocoa-nut palm fruit, a nut, which with its outer husk is almost as large as a peck measure, and that of the St. John’s wort or any other of our native wild flowers.

These differences in size have their counterparts in other directions. We generally think of fruits as being soft, luscious, and pleasant to the taste. Many fruits of delightful colour and texture are, however, bitter as gall, and possess highly noxious qualities. I well remember gathering a plateful of rich purple berries from a plant I discovered in one of my childish rambles and carrying them home as a great prize; I was not a little disappointed when I learned that they were the poisonous fruits of the deadly nightshade; their deceitful resemblance to plums, as well as the berries of the woody nightshade to red currants, make these two of our most dangerous native plants.

As offering very distinct contrasts to the above, we may note the dry membranous fruits of many of our forest-trees, the hard nuts of the hazel and walnut and the leathery husk of the chestnut. Again, the shape of fruits is wonderfully diversified. We have round and oval apples, plums, and gooseberries; the linear seed-pods of the cabbage, cauliflower, wallflower, peas and beans, and other plants in endless varieties of forms.

There are contrasts again in the smooth surface of some fruits and the hairy coats of others where the roughness is due to hooks, prickles and other contrivances. How different, too, is the airy pappus of the dandelion to those heavy fruits which drop like stones and are to be found lying exactly beneath the branches where they have ripened.

These differences in external form are multiplied when we examine fruit more minutely. We shall then find a useful dividing line in the manner in which fruits allow their seeds to escape. In one large division the fruit when perfectly ripe splits open and allows the seed to fall out; such fruits are termed dehiscent (from _dehisco_, I gape). In the other division the fruit remains closed, and the substance of it must decay before the seeds can escape and grow; these are classed as indehiscent (I gape not). Before referring to a few examples of each division we will endeavour to distinguish clearly the various parts of a fruit and learn their proper botanical names.

We must be careful not to confound the seed and the coats of the ovary; the latter is termed the pericarp (_peri_, around, _karpos_, a fruit). In some fruits this pericarp is developed into distinct coats, or layers. In a peach, for instance, the outer coat is rough and hairy, this is called the epicarp (1) (_epi_, upon, _karpos_, a fruit); the middle coat is the succulent delicious fruit, and is known as the mesocarp (2) (_mesos_, middle, _karpos_, fruit), whilst the inner coat is the hard stone, or endocarp (3) (_endon_, within, _karpos_, fruit), and inside it lies the kernel, or true seed. As a type of a dehiscent fruit we may select a pea-pod; here we get no division of the coats into distinct parts, the pericarp is dry and tough, and when perfectly ripe it bursts open, and allows the seeds to escape.

It would be very interesting to make a collection of various seed-vessels, and note the immense variety of ways in which the seeds find their way out of the dry capsules. A poppy-head, campanula and antirrhinum sprays, henbane, columbine, stramonium, and many other plants afford good examples.

The woody pear is the hard fruit of a New Holland plant which splits open to release the seeds. The horse-chestnut is a conspicuous instance of a dehiscing fruit, the rough prickly part is the pericarp, and when the fruit is mature this splits open and allows the two large chestnuts (seeds) to escape. In the sweet-chestnut we get an altogether different structure. If we pick up one of its spiny burrs, we hold in our hand what is called in botany an involucre (from _involucrum_, a cover), that is, a number of bracts which have grown together and formed an outer case to the fruit. The acorn-cup is an involucre, and we may find other good examples in composite flowers and those of the umbelliferæ. The small green whorl in which a daisy-flower is set is, therefore, not a calyx, but an involucre consisting of minute bracts grown together. The true fruit of the sweet-chestnut is enclosed in a mass of spiny bracts, and thus differs entirely from the pericarp of the horse-chestnut; if we wish to speak of it correctly we must call it either a cupule or involucre. We will now select a few examples of fruits that are indehiscent.

On the outside of an orange we find the yellow coat of the pericarp, next to it is the white mesocarp, and inside is the juicy endocarp,[19] in which the seeds are embedded. When an orange falls to the ground these different coats simply decay, and the seeds are aided in their efforts to grow by the succulent flesh of the fruit, which affords them moisture and nutriment. The hazel-nut is a fruit of another texture altogether. The hard shell is the pericarp, and the one or two seeds within it must remain enclosed there until the shell decays and the kernels can germinate and become new plants.

[19] Strictly speaking, the endocarp of the orange is a thin membrane, and the pulp grows from it and fills up the ovary cavities.

In the currant, gooseberry, and date we find examples of indehiscent fruits with a sweet fleshy pericarp. In the date there is only one seed in each fruit, and a curious thin endocarp can be observed enveloping the solitary seed. Many allied species, as well as the date, possess this sweet pericarp, which must decay in order to liberate the seeds, and in the case of succulent fruits the process is frequently assisted by the fruit-eating birds.

It may be well to draw attention to the very simple kind of fruit possessed by the buttercup and other similar plants. It is a dry membranous pericarp, and inside one seed exists free from the pericarp; this remains closed, like other forms of the indehiscent types, and technically this fruit is known as an achene (from _achanes_, not gaping), and it is well named, as it remains closed until decay enables the growing radicle to break through the pericarp and enter the ground. The curious after-development of the strawberry fruit is worth a little careful study.

This flower is known as apocarpous (_apo_, apart, _karpos_, fruit), consisting of a number of distinct ovaries each with one ovule; these ovaries when ripe are exactly like the achenes of the buttercup, but they are developed upon a receptacle which, when fertilisation has taken place, begins to dilate and swell, with the result that the little achenes are gradually scattered over the surface of a large fleshy receptacle which, as it nears its time of perfection, becomes of a most tempting crimson colour. The little seed-like dots we notice on the strawberry are distinct and perfect fruits embedded in a sweet succulent floral receptacle. Thus we find that the strawberry, speaking botanically, is not a berry, but a collection of achenes, the term “berry” being usually restricted to such fruits as the currant and gooseberry. For this reason the strawberry and the common fig are sometimes termed spurious fruits, for in these the soft pulpy flesh is really the receptacle and the little round so-called seeds are the true fruit.

There is a very different formation in the pineapple, since this fruit is the development of an entire spike of flowers; these in their early stage are crowded together on the flower stalk, but as time goes on they coalesce and fuse, with their ovaries, bracts, and receptacles, into a succulent mass, the various parts of which can be well defined if we cut a section through a pineapple before it is quite ripe.

This chapter may fittingly conclude with a brief reference to the ultimate purpose of these varied forms and textures of fruit, for that they each have their special work, and that there is a meaning for every form, is a truism we may accept without doubt. The fruit is in reality the storehouse for the seeds, the latter being the vital part of the plant. If we review the life-history of a plant, first its producing flowers, then the special and intricate processes of pollination and fertilisation, and subsequently the growth of that wonderful little part, the ovule, into a seed, and further if we reflect that the whole strength of the plant has been concentrated on producing that seed, we shall then comprehend the true significance of fruit.

The seed is first stored up in the recesses of the ovary; clearly then the ovary, which subsequently becomes the fruit (pericarp), is intended to protect the seeds, and it is interesting to note some of the various ways in which this protection is afforded. Take first the soft and sweet fruits so plentiful in the autumn; this edible sweet flesh is not developed until the seeds are quite ripe. All through the period of growth and ripening the pericarp is hard or stringy or it may be also sour or acid. This is especially true of hedgerow fruit, such as crab-apples, sloes, and wild pears, texture and juice alike affording complete protection.

Again, such fruit as the walnut and chestnut are protected by their rough covering and hard shells, and many others have their outer coats covered with prickles and spines for the same reason. The most extreme case is perhaps that of _Mucuna pruriens_, a leguminous climber found in the tropics; this has downy pods not unlike those of a sweet-pea, and these pods are covered with brownish hairs which, if incautiously touched, enter the pores of the skin and cause a most intolerable irritation; a truly formidable protection this to the seed.

Let me now point out how the seed is protected in some of the pine family (firs), where there is no pericarp. During the growth and development of the pine seeds, the woody cone is rich in resin, and should an enterprising nuthatch try to peck out the seeds, he finds his beak covered with the resin and his effort baffled.

Protection is also afforded to the seed by the movements of fruit after fertilisation, and of this the cyclamen flower affords a good illustration. As soon as fertilisation has taken place the flower stalk coils up like a watch-spring, and the seed-pod is thus placed safely beneath the leaves to ripen.

In crevices of old walls we may often find that charming little wilding, the ivy-leaved toad-flax; it has a highly intelligent method of protecting its seeds. When the flower is fertilised its stalk bends its point round to the wall, and places the tiny ovary in a cranny of the brickwork to mature and ripen its seeds. These are but two instances, out of hundreds, of plants whose fruits are protected by what we call instinctive movements.

It is of essential importance to young seedlings that they should have sufficient soil, light, and air, to ensure their healthy growth. To begin life directly under the leaves of the parent plant is to court failure and starvation, and so we find in the fruit that wonderful provisions are made to ensure the dispersion of the seed when it leaves the parent plant, and so endless are the contrivances for the dispersion of fruits and seeds, that it will be needful to devote the next chapter entirely to that subject.

Objects to collect and examine:—Compare various fruits, fir-cone, banana, acorn, seeds, and berries, &c. Examine a peach and pea-pod. Collect seed-vessels, horse-chestnut, sweet-chestnut, daisy-flower, orange, hazel-nut, date-fruit, strawberry, pineapple.

Observe seed coverings, pine-cones, cyclamen stems after flowering, seed capsules of ivy-leaved toad-flax in wall crevices.

CHAPTER X

_DISPERSION OF FRUITS AND SEEDS_

“Who gave the thistle’s feather’d seed its plumes,
That wing-like waft it on each gentle breeze
To sterile yet to it congenial soils,
Investing them with purple beauty, rife
With fragrant treasures for the wild bees’ store?”

+T. L. Meritt.+