248 CONCLUDING REMAKES CHAP. VI 



seeds produced by the two or three forms often differ 

 in number, and sometimes in size and weight; thus, 

 five seeds from the long-styled form of Lythrum soli- 

 caria equal in weight six from the mid-styled and 

 seven from the short-styled form. Lastly, short-styled 

 plants of Pulmonaria officinalis bear a larger number 

 of flowers, and these set a larger proportional number 

 of fruit, which however yield a lower average number 

 of seed, than the long-styled plants. With hetero- 

 styled plants we thus see in how many and in what 

 important characters the forms of the same undoubted 

 species often differ from one another characters which 

 with ordinary plants would be amply sufficient to dis- 

 tinguish species of the same genus. 



As the pollen-grains of ordinary species belonging 

 to the same genus generally resemble one another 

 closely in all respects, it is worth while to show, in the 

 following table (34), the difference in diameter be- 

 tween the grains from the two or three forms of the 

 same heterostyled species in the forty-three cases in 

 which this was ascertained. But it should be observed 

 that some of the following measurements are only 

 approximately accurate, as only a few grains were 

 measured. In several cases, also, the grains had been 

 dried and were then soaked in water. Whenever they 

 were of an elongated shape their longer diameters 

 were measured. The grains from the short-styled 

 plants are invariably larger than those from the long- 

 styled, whenever there is any difference between them. 

 The diameter of the former is represented in the table 

 by the number 100. 



We here see that, with seven or eight exceptions 

 out of the forty-three cases, the pollen-grains from one 

 form are larger than those from the other form of the 

 same species. The extreme difference is as 100 to 55 j 



