[Illustration: Fig. 81. A, ripe carpel of pea or “pea pod.” B, pod suddenly split and twisted up, scattering the seeds.]
Let us pick a nearly ripe pea-pod and examine it; it is the ripe carpel, with several ripe seeds in it, and together they form what is called a ~fruit~. In the case of the pod the “fruit” itself is a dry pea-pod husk, but in other plants the fruits may be very different. Examine a marrow, for example. Watch it in the course of its growth, if possible, and you will find that the marrow flower is one of those with its seed-box below and outside the calyx and petals. As the marrow ripens this swells with the food stored in it, and the many growing seeds, till the flowers are only small shrivelled structures at one end. If you then cut the ripe, or nearly ripe, marrow fruit across, you will find that its wall is very thick and fleshy, and that the many seeds are buried in a soft pulp. The melon shows us just the same thing. Such fruits seldom split suddenly to shoot out their seeds (though some foreign ones do); they depend more on animals which may eat them and so scatter the seeds about.
In all cases it is better for the plant to have the seeds scattered so that they do not sprout too near together, but have room enough to grow without crowding each other out.
In the pea and marrow there are many seeds, but there are large numbers of fruits in which we find only one. For example, in plums, cherries, and peaches we have a fleshy outer fruit-case with a stony lining covering over one large seed. Such fruits do not open, for there is only one seed within, and so the fruit is scattered whole. These fruits nearly always get scattered by animals, for the flesh is very sweet and attractive to eat, and then, as a rule, they get rid of the stone (which contains the seed) at some distance from the parent.
[Illustration: Fig. 82. Cherry fruit cut open, showing the flesh (~f~), stone (~s~), and seed S.]
Sometimes we find a number of fruits just like the cherry clustered together, only instead of each of them being large, they are all very small, so that the whole cluster of fruits may be the size of a single cherry. This is the case in the common blackberry and the raspberry, where each of the little fruitlets really corresponds to a cherry.