Fig. 51. The outer leaflike tubular or hooded spathe surrounds in our common Jack-in-the-Pulpit a clublike spadix, upon which are crowded the tiny flowers.
No feature of a landscape gives us more pleasure than its flowers, over which poets have sung and artists have painted their most charming pictures, even a musician has composed a very beautiful piano piece, “To a Water Lily.” But their true place in the scheme of nature has a deeper significance: the wonderful color and symmetry of their parts, the plan of their arrangement, their transformation into curious forms, like the Madagascar orchid, and hundreds of others—all these point to their supreme function, an act of self-sacrifice comparable only to the fall of a leaf when its task is done. Petals, too, wither and die when the fertilized ovary, already a mother, begins the slow process of maturing its young and the end of the flowering stage is reached. Such a climax is this in certain plants that the whole plant dies, as we have already noted in the case of the century plant. The toddy or wine palm of India, often sixty or seventy years old and more than a hundred feet tall, flowers only once, and, as if in recognition of the fact that it has done that for which it grew, slowly dies as the seed ripens. More humble annuals, like buckwheat, and hundreds of others, live only one brief growing season, produce flowers and seeds, and then die, leaving behind them the only means of perpetuating their kind. The dormant seed carries over the winter the life they were themselves unable to maintain, as perennials and woody plants do in their buds.
THE FRUIT
The number of different kinds of fruits that one can buy even in the greatest markets in the world is so small, compared to all fruits that are annually produced by plants, that they might almost be likened to an ear of corn as against a Missouri cornfield. If, as we have seen, all flowering plants must produce fruits, then what we commonly call such can be only a fraction of what actually makes up nature’s annual harvest. It follows that fruits often occur in unfamiliar disguises and, as we shall see presently, some of the things we have been calling fruits may be so only partly, if at all.
Disregarding what we call fruits and looking at it from the plant’s point of view, a fruit is anything in which, or upon which, a seed is developed or ripened quite without regard as to whether it is edible by man or not. As the ovary is the female organ of reproduction and contains the yet undeveloped seed, it follows also that fruits are practically always a development of some part or modification of the ovary or the upper end of the flower stalk upon which it rests and from which it is often scarcely separable.
Familiar enough is the distinction between dry fruits, such as a pea pod and fleshy ones like oranges, and this quality of being fleshy or dry is practically universal. Among fleshy fruits a few well-known types may be mentioned, such as the orange, tomato, grape, gooseberry, and cranberry, all true berries. There are, of course, thousands of less familiar examples of berries, but, whether with a hard rind as in the orange or not, they are a direct development, or often a mere swelling of the ovary, with sometimes the adhering calyx, and contain the seed. In apples and pears, known as pomes, the fleshy part is a development of part calyx and part the receptacle upon which the ovary is supported while still in the flower. The ovary in these fruits is the parchmentlike interior which contains the seed. Plums and cherries, which have a single stone, instead of numerous seeds buried in the flesh, are known as drupes. These familiar examples are matched by thousands of others of which we hear nothing, all drupes and all formed directly from the ripened ovary and without much change, except the increase of size, juiciness and large development of the tiny immature seed, now transformed into a stone. In the watermelon, pumpkin, and related plants, is still another kind of fleshy fruit, called a pepo. All of this, including the hard rind, is transformed ovary and calyx completely incorporated, and forming in the pumpkin perhaps the largest fleshy fruit known. In a considerable number of plants there is not a single ovary, but several, or in some cases many. These occasionally all develop into what is called an aggregate fruit, of which examples are the blackberry, mulberry, magnolia, and many others.
While it would be logical to think that these fleshy fruits were designed to make delicious food for man, that, in the light of what we have seen to be the real function of the flower, is an assumption which, while flattering, is far from the truth. It is much more certain that fleshy fruits help plants in the dispersal of their seeds and that this fleshy, juicy character is just one more device of nature to see to it that not only do plants produce seeds, but that the seeds are carried and so spread the plant over considerable areas. Birds and animals eat such fruits in enormous quantities and, in fact, bird migrations are thought to be not so much response to winter cold as to the fact that fruits are scarce then. When it is remembered that some birds make tremendous flights, often over 10,000 miles in a few days, their capacity to spread seeds through their droppings may be imagined. In the chapter on plant distribution some truly remarkable cases of such seed dispersal will be given.
The chance of having seed carried great distances, because it is embedded in a fleshy, often brightly colored fruit, would seem to put plants having dry fruits at a disadvantage. Birds and animals cannot be expected to look after the dispersal of those fruits that are neither tempting to the sight nor to the taste. And it must be confessed that quite other qualities in dry fruits insure their dispersal. Some are so nutritious, like the acorn, that thrifty squirrels store them over the winter, as they do many other seeds which are harvested from dry fruits. Various grains are often so stored by man, and rice, wheat, buckwheat, and other cereals are common cases. In nearly all grains the seed fills so completely the fruit that cereals are very generally, but mistakenly, called seeds. A grain of wheat or corn is just as complete a fruit as a watermelon. Only its outer coat and inner seed are so closely welded together as not to be usually recognized as a fruit, with the seed inside.