Where the fruits are neither barbed nor very good to eat, and so apparently doomed to be more or less permanent stay-at-homes, nature has provided some of them with the proper equipment for flight through the air. Winged fruits like the maple are to be seen on any windy day during their season scurrying before the breeze, and consequently spreading their kind over considerable distances. In the maple there are two wings, joined at the base where the seeds are embedded in the wings, and the fruit is known as a samara ([Figure 58]), or key fruit, from a slight resemblance to an old-fashioned key. Ash trees bear fruits that are a slight modification of this type and may be carried considerable distances by the wind ([Figure 59]).
In the dandelion, daisy, and nearly all its thousands of relatives, this faculty of setting sail in the air has been carried to the greatest perfection, just as we saw its flowers were. In this family of plants, the largest in the world, the fruit is mostly tipped or surrounded by a small collection of very fine bristles. The fruit, known as an achene ([Figure 56]), is so light that with the added buoyancy of this tiny collection of down it can be transported great distances. Some have been known to fly hundreds of miles in severe storms, and, as we shall see in the chapter on plant distribution, these tiny plant balloons have played a conspicuous part in spreading their kind over the face of the earth. Cat-tails also, together with many other plants, have this faculty and make up by its possession for the lack of fleshy or otherwise desirable fruits that might be carried. All achenes are not winged, those which dot the surface of the strawberry being imbedded in the luscious flesh, which is not really fruit at all. Only the achenes on the strawberry are true fruits, the fleshy part being merely a development of the upper part of the flower stalk and not of the ovary ([Figure 52]).
Fruits, then, cannot be restricted to the common understanding of them. They are transformations of the ovary, in which or upon which seeds are nursed, and upon which most plants depend for the dispersal of their seeds. We shall see later on how fruits have fulfilled their destiny, how some are fit for their true function only when they have been eaten by birds, and when some digestive juice has released them from the impotence they would suffer without being eaten, how a whole forest has been changed in the West by the busy activity of squirrels upon the fruits and seeds of a single kind of fir tree; how the fruit of the coconut palm has been spread throughout the tropical world because it can float in the sea securely protected from injury from salt by the impervious coverings of its fruits.
THE SEED
As the final stage in the development of all plants is their seed, with the dropping of which they bid good-by to their fellows, it is not perhaps remarkable that in the seed of all flowering plants is the germ for the new generation. To seeds which may be as small as the mustard, so often mentioned in the Bible, or as large as the coco de mer, or double coconut, from the Seychelles Islands, often fifty pounds or over, is intrusted by cunning nature the one final and most important act in the whole kingdom of the plant world. Nearly all plants would die off forever if seeds did not have in them the germ of life, apparently quite dead, but actually only dormant. This living germ may persist for years, sometimes even a hundred years, and yet with the proper conditions it never fails to sprout.
Seeds have inside them a tiny plantlet folded and ready to grow when the seed splits to release it. Also, in the seed is stored up food to sustain the new plant until such time as its own roots begin to act. This young plantlet is known as the embryo, and to this all actions of the seed are subservient.
As the seed splits, and the young plant develops its first leaves and rootlets, there is shown one of the most remarkably uniform tendencies in plant life. In all plants with net-veined leaves the young plantlet starts life with two leaves, or cotyledons, as these first leaves are called, and this whole group of plants are thus known as dicotyledons. In plants with parallel-veined leaves the young plantlets start out with a single cotyledon and are therefore called monocotyledons. In only the pines, spruce, and a few other evergreen trees the seedling plants have several cotyledons and are known as polycotyledons. All the flowering plants in the world belong to one of these groups, so that merely to see the germinating seed tells the story at once. The linking of parallel-veined leaves and a single seed leaf, and net-veined leaves with two seed leaves, is also associated with very definite arrangement of their flower parts, their method of growth and other characters. Something has already been said of this in the discussion of stems and leaves, and more will be found in the chapter on plant families. No more beautiful example of the plan or scheme of nature is to be found than these characteristics of all plants, and in seeds we find the first hint as to which army the plant will join, under which banner it will fight, and under what generalship it will develop. Nothing tells us so much as these first seed leaves, pushing their way up through the soil and revealing, as they burst above ground, to what place in nature their destiny will consign them.
Flowering plants, which make up the bulk of the vegetation of the earth, have been discussed in some detail, not only because they furnish us with all the things that make life possible, but also because they show perhaps better than anything else the division of labor, all striving for one end. Roots, the food gatherers. Stems, the framework for the foliage and its means of reaching the light, or as a storage house for reserve food. Leaves of many kinds, all factories working night and day to make the necessary food. Flowers of every hue and shape to lure insects, or by other means secure union of male and female. Fruits to ripen the result of this mating of the sexes. And, finally, the seed carrying with it the yet unborn life. Each part occasionally losing itself in order that the end may be accomplished, many of them changing their form or even their function where that is of advantage, all in their separate ways doing their task, the end of which they cannot see, and the fruits of which they will never enjoy. Nowhere is it so true as in plants that to save oneself there must be the capacity to give oneself. Untold millions of leaves fall, or trees crash down, or seeds are developed, each fulfilling their destiny which is to insure the perpetuation of their kind. As we shall see later on, there are many mistakes, many apparently futile attempts, thousands are wiped out that one may be saved, and in the past multitudes have gone out forever. Yet the result of it all is the plant world as we know it to-day, each kind struggling to increase its sphere of influence, or to cover more of the earth’s area. The combat between different kinds is inexorable, yet the capacity for sacrifice on the part of different organs, in order that a certain individual kind may win, is literally beyond belief.
2. Flowerless Plants
In the light of what has been said about flowers it may well be questioned how anything can be a plant and still have no flower. The fact is that flowers as we commonly understand them are unknown in the plants about to be discussed, but that what corresponds to a flower, and performs the function of a flower all plants must and do have. In the case of most flowering plants the possession of flowers is one of the beauties of nature in its most resplendent mood, while in the so-called flowerless plants the functions of flowers are performed by tiny microscopic organs, even the existence of which has been only recently discovered. Because flowering plants produce their sexual organs in such a gorgeous setting, for all the world to see their matings they have been called phanerogams, which means literally visible marriage, while the flowerless plants which perform similar functions in more secret ways are called cryptogams, meaning hidden marriage.