Chap. IV. PONTEDERIA. 155 



above the middle of the corolla, and nearly on a level 

 with the mid-length stamens in the other two forms: 

 its summit is a little bent upwards. In the short- 

 styled form the pistil is, as we have seen, very short, 

 and differs from that in the other two forms in being 

 straight. It stands rather beneath the level of the 

 anthers of the shortest stamens in the long-styled and 

 mid-styled forms. The three anthers of each set of 

 stamens, more especially those of the shortest stamens, 

 are placed one beneath the other, and the ends of the 

 filaments are bowed a little upwards, so that the pollen 

 from all the anthers would be effectivelv brushed off 

 by the proboscis of a visiting insect. The relative 

 diameters of the pollen-grains, after having been long 

 soaked in water, are given in the following list, as 

 measured by my son Francis :• 



Long-styled form, from the mid-length stamens . 



(Average of 20 measurements. 

 " " from the shortest stamens . . 



(10 measurements.) 

 Mid-styled form, from the longest stamens . . . 



(15 measurements.) 

 " " from the shortest stamens . . 



(20 measurements.) 

 Short-styled form, from the longest stamens . . . 



(20 measurements.) 

 " " from the mid-length stamens . 



(20 measurements.) 



Divisions of the 

 Micrometer. 



13.2 



9.0 



16.4 



9.1 



14.6 



12.3 



We have here the usual rule of the grains from the 

 longer stamens, the tubes of which have to penetrate 

 the longer pistil, being larger than those from the 

 stamens of less length. The extreme difference in 

 diameter between the grains from the longest stamens 

 of the mid-styled form, and from the shortest stamens 

 of the long-styled, is as 16.4 to 9.0, or as 100 to 55; 



