chap.vi. on heterostyled plants. 249 



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

 five seeds from the long-styled form of Ly thrum sali- 

 caria equal in weight six from the mid-styled and seven 

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

 of Pulmonaria offlcinalis bear a larger number of flow- 

 ers, and these set a larger proportional number of fruit, 

 which however yield a lower average number of seed, 

 than the long-styled plants. With heterostyled plants 

 we thus see in how many and in what important char- 

 acters the forms of the same undoubted species often 

 differ from one another — characters which with ordinary 

 plants would be amply sufficient to distinguish 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-five cases in 

 which this was ascertained. But it should be observed 

 that some of the following measurements are only 

 approximately accurate, as onl}"^ 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, when- 

 ever there is any difference between them. The diam- 

 eter 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, 

 and we should bear in mind that in the case of 



