Some fruits are covered with spines and hooks, which catch on to the wool of animals, and so get carried quite a distance before they are dropped. This gives the seedlings a good chance of reaching a new spot where they can grow away from the parent, and so not be too crowded. Well-known fruits of this kind are the burs, which stick tightly to one another with their dozens of little hooks, the “bur” being really a cluster of many fruits together. Simple fruits of the same kind are the bidens, each with its two long spines, and the small fruits of the goose grass, which are covered with the finest hooks.
[Illustration: Fig. 86. A Bur, which is a cluster of hooked fruits.]
[Illustration: Fig. 87. Simple fruits: (~a~) of the Goose grass with its hooks; (~b~) the Bidens with its harpoon-like spines.]
[Illustration: Fig. 88. Strawberry. Each of the little “seeds” is a whole fruit, and the “flesh” the swollen receptacle.]
Quite a special kind of fruit is the ~strawberry~, which, as you know, has a thick fleshy pulp covered with a number of small, yellow “seeds.” In reality, each of these “seeds” is a whole fruit, and the thick flesh which we eat is the swollen end of the flower stalk which we call the “receptacle.” Therefore ~a strawberry really consists of a large number of fruits~ and a piece of stalk which is altered to form the fleshy, attractive mass which induces birds and people to eat the whole, and so scatter the little dry fruits.
There are very many other kinds of fruits which all have special devices to make sure that their seeds are scattered, and all proper fruits have seeds in them. But, just as we found that some garden flowers are grown only for their beauty, and do not set any seed, so we find that some fruits are grown specially without any seeds, such as bananas and some oranges. Such fruits are the result of our liking to eat the soft, sweet pulp without the trouble of the seeds, but such fruits are of no use to the plant.
Now let us look at the structure of the ripe seeds themselves, and see how they are fitted to go out alone into the world prepared to make a new plant. Seeds are all very much alike in the important points of their structure, although they vary much in the shape, size, and colour of their parts. We already know what beans are like from our careful study of them at the beginning of our work (~see~ Chapter III.), and beans show us particularly well all the important parts of a true seed, so that we may take them as being typical of one large family of flowering plants. The maize embryo (~see~ p. 10) is typical of the rest of the flowering plants. ~In the ripe seeds~ of both of these groups (you should examine them again if you have forgotten any of the facts) we find that ~the important thing is the baby plant~, which is supplied with food and ~protected by two seed coats~, till it is time for it to grow out and form a new plant like its parent.