THE POLLINATION OF VALLISNERIA SPIRALIS 



Robert B. Wylie 



(WITH PLATE IX AND SIX FIGURES) 



Vallisneria has long been counted one of the classic examples 

 of cross-pollination. Living vegetatively as a submersed aquatic, 

 its dioecious flowers are brought together at the surface of the water 

 in most ingenious fashion. These highly specialized flowers present 

 the strongest contrasts, not only in size and structure, but in 

 behavior as well, and give this plant its rank as one of the climax 

 types with respect to floral differentiation. Specializations of 

 such evident advantage for cross-pollination in a form so admirably 

 situated for vegetative propagation seem to emphasize the impor- 

 tance of sexuality, or at least of seed production, in the higher 

 plants. 



While the general method of pollination in Vallisneria is well 

 known, many interesting facts seem never to have been published, 

 and the underlying principle has not been emphasized. The 

 figures current in textbooks are highly generalized, and some of 

 them are far from accurate. The story which they are intended 

 to illustrate is likewise incomplete or in some cases highly distorted. 

 In any event, neither figure nor story has done justice to the inti- 

 mate history of pollen transfer in this remarkable plant. 



It will be noted at once that the following account diverges 

 radically from that suggested by Kerner's (i) beautiful and 

 widely copied figure. A comparison shows that these differences 

 relate not only to the size and structure of the flowers, but are even 

 more fundamental in character. Kerner emphasizes the fact 

 that pollination is brought about through the contact of flowers 

 floating on a level water surface; there follows an outline of a 

 method of pollen transfer through the special agency of the surface 

 film of water. The general drawing (pi. IX) is based on photo- 

 graphs of living flowers, measurements, and camera drawings of 

 parts. 



135J 



[Botanical Gazette, vol. 63 



