CHAP. IV. PONTEDERIA. 187 



in both sets of anthers in the short-styled form being 

 smaller than those from the corresponding anthers in 

 the other two forms ; and here we have a case parallel 

 with that of the mid-styled form of Lythrum salicaria. 

 In this latter plant the pollen-grains of the mid-styled 

 forms are of smaller size and have less fertilising power 

 than the corresponding ones in the other two forms ; 

 whilst the ovarium, however fertilised, yields a greater 

 number of seeds ; so that the mid-styled form is alto- 

 gether more feminine in nature than the other two 

 forms. In the case of Pontederia, the ovarium in- 

 cludes only a single ovule, and what the meaning of 

 the difference in size between the pollen-grains from 

 the corresponding sets of anthers may be, I will not 

 pretend to conjecture. 



The clear evidence that the species just described is 

 heterostyled and trimorphic is the more valuable as 

 there is some doubt with respect to P. cordata, an in- 

 habitant of the United States. Mr. Leggett suspects* 

 that it is either dimorphic or trimorphic, for the 

 pollen-grains of the longer stamens are "more than 

 twice the diameter or than eight times the mass of 

 the grains of the shorter stamens. Though minute, 

 these smaller grains seem as perfect as the larger 

 ones." On the other hand, he says that in all the 

 mature flowers, " the style was as long at least as 

 the longer stamens ;" " whilst in the young flowers 

 it was intermediate in length between the two sets of 

 stamens ;" and if this be so, the species can hardly be 

 heterostyled. 



' Bull, of the Torrey Botanical Club,' 1875, vol. vi. p. 62. 



