140 THE FLOWERING PLANT. 



PHYSIOLOGY. 



Protection of seeds, during the early period of their growth, is 

 largely effected by the perianth ; and the calyx, especially when 

 gamosepalous, often persists and surrounds the fruit. A protec- 

 tive function may also be assumed by bracts, as in sweet chestnut 

 and beech. Seeds are also frequently provided with hard coats, 

 and, when this is not the case, all or part of the pericarp serves 

 the same end, e.g., in dry indehiscent and stone fruits. Succulent 

 fruits, again, are almost inedible till ripe, when, as we shall see, 

 they lay themselves out to be eaten, so to speak. In water plants 

 the seeds generally remain protected in the mud at the bottom 

 till ready to germinate. Vallisneria is a very interesting plant in 

 this respect. The spiral stalk (cf. p. 115) of the female flower 

 coils up after pollination, drawing it down to a place of compara- 

 tive safety for the ripening seeds. Such protective movements 

 are also known in some land plants. The stalk of Cyclamen or 

 sowbread coils up spirally, and the peduncle of dandelion moves so 

 as to bring the ripening fruit close to the ground. 



Distribution of fruits and seeds is brought about in a variety 

 of ways. In comparatively few cases is there any special provision 

 for setting the seeds close to the parent plant. Some forms, 

 however, are heterocarpic, i.e., producing two kinds of fruit, one 

 of which is suitable for this purpose. There is, for example, a 

 kind of vetch which produces, in addition to the ordinary pods, 

 small pointed ones, which grow near the ground, and are forced 

 into it by the growth of their stalks. The capsules produced by 

 the cleistogamous flowers of sweet violet are also situated near the 

 ground. As a general rule, however, there are special arrange- 

 ments for dispersing the seeds and fruits to a distance. The 

 chief agents for effecting this are — (1) the plant itself, (2) water, 

 (3) wind, and (4) animals. 



(1.) The plant itself distributes its seeds in many forms, usually 

 as a result of the elasticity of the fruit, which in this case is 

 either a splitting fruit or else dry and dehiscent. In geraniums 

 we have an example of the former kind (fig. 57). The axis of 

 the fruit is here produced into a kind of beak, at the base of 

 which are five distinct lobes, each attached by a thin elastic rod 

 to the beak. When the fruit is ripe these rods suddenly curl up, 

 and the lobes (or seeds they contain) are detached and thrown to 

 a considerable distance. The same kind of thing takes place in 

 balsam (hence called scientifically Imyatiens noli me tangere). 



The legumes of some plants, such as vetch and broom, split 

 violently open when ripe, and violently eject their seeds. A 



