28 ORGANIC BEHAVIOUR 
the expulsion of water from certain cells at the point of 
insertion of the leaflets or leaf-stalks, rendering them flaccid. 
Appealing even more strongly to the popular imagination, 
though probably not of deeper biological significance, is the 
behaviour of plants in relation to the essential process of 
fertilization. Only two examples can here be cited. Valisneria 
spiralis is an aquatic plant, with long submerged strap-like 
leaves, which grows in still water in Southern Europe. The 
female flower is enclosed in two translucent bracts, which 
form a protective bladder so long as the flower is beneath 
Fic. 8.—F lower of Valisneria. 
the surface of the water; but the flower-stalk continues to 
grow until the flower reaches the surface, when it becomes 
freely exposed by the splitting of the bracts. There are three 
boat-shaped sepals, which act as floats; three quite minute 
petals ; and three large fringed stigmas, which project over the 
abortive petals in the space between the boat-like sepals. The 
flower is now ready for fertilization. 
The male flowers, which are developed on different indi- 
viduals from those which produce the female flowers, grow in 
bunches beneath an investing bladder. The stalk does not 
clongate, so that the bladder never rises far above the bottom, 
and remains completely submerged. Here the bladder bursts, 
and the male flowers, with short stalks, are detached. Each 
has three sepals, which enclose and protect the stamens. The 
separated flower now ascends to the surface, the sepals open 
