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, t.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. Asa 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 Impatiens noli me tangere). 
The legumes of some plants, such as vetch and broom, split 
violently open when ripe, and forcibly eject their seeds. A 
