186 HETEEOSTYLED TEIMOEPHIC PLANTS. Chap. IV. 



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 effectively 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 



u-e 



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 ; 

 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 



