xviii] HYDROPHILOUS POLLINATION 235 



the water surface, is no more truly aquatic than are the vital 

 processes of a man in a diving bell, since, as Hooker points 

 out in the case of Limosella, the transference of the pollen 

 takes place within a bubble of gas. Certain plants, however, 

 present transitional methods of pollination, which without 

 being actually hydrophilous, show approaches to this state. 

 The oft-quoted case of Vallisneria spiralis (Hydrocharitaceae) 

 is perhaps the best instance of such a transitional method. The 

 male and female plants are distinct. The female flowers are 

 solitary within a spathe, and are carried up to the surface of the 

 water by the elongation of the peduncle below the spathe. 

 When mature they lie horizontally on the water surface^. The 

 submerged male spathes contain over 2000^ small flowers each 

 with two stamens; the perianths are hermetically sealed, each 

 enclosing a bubble of air. These male flowers become detached 

 and rise to the surface of the water, where they open. The float- 

 ing male flowers were figured early in the eighteenth century 

 by Micheli^, an Italian botanist. A later observer in India* 

 speaks of " seeing under a noonday sun the innumerable florets 

 freed from their spathes and ascending like tiny air-globules 

 till they reach the surface of the water, where the calyx quickly 

 bursts the two larger and opposite sepals, reflex, forming tiny 

 rudders, with the third and smaller recurved as a miniature sail, 

 conjointly facilitating in an admirable manner the florets' mis- 

 sion to those of the emerging females." The male flowers are 

 thus conveyed over the water surface by air currents, and some 

 of them get carried into the neighbourhood of the female flowers, 

 where the sticky pollen of the dehiscing anthers is likely to be 

 rubbed off against the exposed stigmas. Each female flower, 

 owing to its weight, is surrounded by a minute depression 

 in the surface film of the water; the male flowers easily slide 

 down the slope thus produced, and so approach the female^. 

 After pollination the spiral peduncle contracts, carrying the 

 maturing fruit deep down into the water; it is said that the 



1 Chatin, A. (18552). 2 Wylie, R. B. (191 72). 



3 Micheli, P. A. (1729). Scott, J. (1869). 



sr 



