Fig. 144.—A′, Strawberry; B´, longitudinal section; Ac, carpel, R, swollen receptacle. (× ⅔.)
The fruit of the wild rose.—The fruits of the wild rose are called hips. They are urn-shaped, and on the flat rim of the urn five scars show the former position of the sepals.
In some cases the sepals themselves have remained. The narrower mouth of the urn is filled by a tuft of greyish hairs which, when the fruit is cut open, are seen to be the styles of the carpels. The carpels are hairy, and stand on the bottom and sides of the urn-cavity. Each carpel contains a seed. Comparison with the flower shows that the red, fleshy urn is the developed receptacle.
The strawberry.—In the strawberry ([Fig. 144]) the eatable part of the fruit is again the swollen and juicy receptacle. In this case it has grown up on the inside of the carpels—the little, yellow nutlets (carpels) lying on the surface. Each carpel contains a seed.
Why some fruits are sweet.—The delicious flavours of sweet fruits have been developed as baits for the allurement of such animals as are likely to scatter the seeds to the best advantage. Consider such fruits as cherries, currants, and rose-hips. Birds—such as thrushes—find them very nice to eat, and are ready to carry them away to consume at their leisure. The birds eat the sweet, fleshy part, but in the case of a stone-fruit they drop the stone and leave the seed to germinate. A seed which is in danger of being swallowed is either hairy like the rose-carpels (and therefore rejected because it irritates the mouth unpleasantly), or it is enclosed in a hard or horny case, upon which the animal’s digestive juices are unable to act. When the seed is dropped it is no worse for its experience, and with good luck grows up into a plant.
Fig. 145.—Holly. The red colour of the fruits
contrasts strongly with the dark-green
of the leaves. (× ⅙.)
Eatable fruits generally conspicuous.—In order that birds and other animals may easily find the luscious fruits which they may eat as a reward for scattering the seeds, such fruits are almost always displayed very conspicuously, and are brilliantly coloured. Oranges, plums, red currants, apples, etc., illustrate this fact well. Red is perhaps the commonest colour of eatable fruits, because it contrasts so strongly with the green colour of the foliage ([Fig. 145]).