84 



MH. C. DABWIN OX THE DIMOBPHIC CONDITION 



than the long-stvled forms ; consequently the anticipation that the 

 plants having largely developed pistils with rougher stigmas, and 

 having shorter stamens with smaller pollen-grains, would prove to 

 be more feminine in their nature is exactly the reverse of the 

 truth. If the species of Frimula are tending to become dioicous, 

 which possibly may be the case, the future hypothetical females 

 would have short pistils, and the males would have short stamens ; 

 but this tendency is accompanied, as we shall presently see, by 

 other conditions of the generative system of a much more singular 

 nature. Anyhow, the possibility of a plant thus becoming dioicous 

 by slow degrees is worthy of notice, as the fact would so easily 

 escape observation. 



In 1860 I found that a few umbels of both long-styled and 

 short-styled Cowslips, which were covered by a net, did not pro- 

 duce seed, though other umbels on the same plants, artificially fer- 

 tilized, produced an abundance of seed ; and this fact shows that 

 the mere covering in itself was not injurious. Accordingly, in 

 1861 I covered up under a similar net several plants just before 

 they opened their flowers ; these turned out as follows : — 





No. of 



Plants. 



No. of 

 Umbels 

 produced, 



Product of Seed. \ 



1 



Short-styled .... 



6 



18 



2i 

 74 



1-3 grains, or 50 seeds.' 

 Not one seed. | 



Long-styled 



Judging from the exposed plants which grew all round in the 

 same bed, and had been treated in every way exactly the same, 

 except that they were exposed to the visits of insects, the six short- 

 styled plants ought to have produced 92 grains' weight of seed in- 

 stead of only 1-3 ; and the eighteen long-styled plants, which pro- 

 duced not one seed, ought to have produced above 200 grains' 

 weight. The production of the 1-3 grain of seed in the smaller 

 lot was probably duo to the action of Thrips or some minute in- 

 sect. This evidence is sufficient, but I may add that ten pots of 

 Polyanthuses and Cowslips of both forms, protected from insects 

 in my greenhouse, did not set one pod, though artificially fertilized 

 flowers in other pots produced an abundance. So we see that the 

 visits of insects are absolutely necessary to the fertilization of 

 Cowslips. As the exposed plants produced an abundance of seed, 

 the tendency to a dioicous condition, previously remarked on, 

 might have been safely carried on, as we see that there is an effect- 



