186 HETEROSTYLED TEIMORPHIC PLANTS. Chap. IV. 



and this is the greatest difference observed by me in 

 any heterostyled plant. It is a singular fact that the 

 grains from the corresponding longest stamens in the 

 two forms differ considerably in diameter; as do those 

 in a lesser degree from the corresponding mid-length 

 stamens in the two forms; whilst those from the cor- 

 responding shortest stamens in the long- and mid- 

 styled forms are almost exactly equal. Their in- 

 equality in the two first cases depends on the grains 

 in both sets of anthers in the sh(^rt-styled form being 

 smaller than those from the corresponding anthers in 

 the other two forms; and here we hve 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-gi-ains from 

 the corresponding sets of anthers may be, I will not pre- 

 tend 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 



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



