40 HETEBOSTYLED DIMOKPHIO PLANTS. Chap. I. 



The fertility, therefore, of the two legitimate unions 

 together to that of the two illegitimate unions, as judged 

 by the proportional number of flowers which yielded 

 capsules, is as 100 to 84. Judging by the average 

 weight of seeds per capsule produced by the two kinds 

 of unions, the ratio is as 100 to 63. On another occa- 

 sion a large number of flowers of both forms were 

 fertilised in the same manner, but no account of their 

 number was kept. The seeds, however, were carefully 

 counted, and the averages are shown in the right-hand 

 column. The ratio for the number of seeds produced 

 by the two legitimate compared with the two illegiti- 

 mate unions is here 100 to 53, which is probably more 

 accurate than the foregoing one of 100 to 63. 



Hildebrand in the paper above referred to gives the 

 results of his experiments on the present species ; and 

 these are shown in a condensed form in the following 

 table (11). Besides using for the illegitimate unions 

 pollen from a distinct plant of the same form, as was 

 always done by me, he tried, in addition, the effects of 

 the plant's own pollen. He counted the seeds. 



It is remarkable that here all the flowers which 

 were fertilised legitimately, as well as those fertilised 

 illegitimately with pollen from a distinct plant be- 

 longing to the same form, yielded capsules ; and from 

 this fact it might be inferred that the two forms were 

 reciprocally much more fertile in his case than in 

 mine. But his illegitimately fertilised capsules from 

 both forms contained fewer seeds relatively to the 

 legitimately fertilised capsules than in my experi- 

 ments ; for the ratio in his case is as 42 to 100, 

 instead of, as in mine, as 58 to 100. Fertility is a 

 very variable element with most plants, being deter- 

 mined by the conditions to which they are subjected, of 

 which fact 1 have observed striking instances with the 



