CERATOPHYLLACEAE 391 



much more numerous than the female. These possess a polyphyllous perianth 

 surrounding an ovoid ovary with a style projecting beyond the perianth to a distance 

 of four to five times the length of the latter ; it is bent downwards like a hook, and 

 tapers towards the point: this is not papillose, but its whole lower side, which 

 secretes a sticky substance, serves as a stigma. 



The male inflorescence consists of 12-16 very short-stalked anthers, which are 

 enclosed in a polymerous involucre. Each stamen is made up of a short filament, 

 and two anther-lobes, opening laterally by longitudinal slits, and composed at the tip 

 of loose, air-containing tissue produced into two small, thorn-like processes curved 

 towards the middle, between which there is generally a blackish, more or less vertical, 

 tubercle-like gland. Stahl (' Pfl. u. Schnecken ') says that these apical appendages 

 of the stamens contain tannin, and form an effective protection against water-snails 

 and other vegetarian aquatic creatures. Ludwig has described the cellular tissue 

 found below these points as a ' float ', as it makes the whole stamen specifically 

 lighter than water, and therefore carries it to the surface, when it is freed from the 

 flower. The round or long pollen-grains are surrounded by a delicate membrane 

 only, and possess no extine. Their specific gravity is exactly the same as that of 

 water, so that they float at any depth. This varying specific gravity of the pollen- 

 grains and the whole pollen-bearing mechanism, together with the retention of the 

 stiff-leaved involucre, determines the method of transport of pollen. The involucral 

 bracts have a tendency to bend inwards (on empty inflorescences they are vertical), 

 so that the stamens have not enough room when fully mature. When the anthers 

 dehisce, the stamens are forced out of the involucre and come to the surface by 

 the help of the ' float,' or, as more frequently happens, are held back between 

 the hooked leaves of the upper nodes. During this upward movement the anthers 

 dehisce, being greatly assisted in this by the vertical position of the stamen main- 

 tained by the ' float ' ; the pollen, being of the same specific gravity as the water, 

 spreads over the whole space touched by the stamens ; the water, therefore, in which 

 the plant grows, is everywhere full of the large pollen-grains (40-50 /x broad and 

 50-75 /u, long). The peculiar movement of the stem is useful in the spreading of 

 pollen, particularly in still water, where it is of inestimable value. E. Rodier first 

 described this movement as follows. — The young flower-bearing internodes move 

 independently of light, the stems as a rule bending from right to left in the 

 morning and from left to right after midday. Sometimes in six hours angles 

 of 200° are described. Besides this the branches undergo twisting movements 

 around their axis of growth. The stem begins to bend at the tip, continuing 

 downwards with decreasing strength, while the backward movement begins at the 

 base and works upwards, so that the last internodes, just before bending backwards, 

 sometimes form an acute angle with the axis. As pollen is formed very abundantly, 

 the movements just described ensure the pollination of the long, filiform stigmas 

 of the female flowers, which mature somewhat before the anthers. F. Ludwig did 

 not observe the simultaneous movement of female flowers towards the surface 

 (mentioned by Hermann Beyer), on which the pollen last dehisced floats. 



2598. C. submersum L. — The mechanism of this species agrees with that 

 of the preceding one. 



