320 ORIGIN OF SPECIES 



pollen; so it is with the pollen of the several forms of the 

 same species, for legitimate pollen is strongly prepotent over 

 illegitimate pollen, when both are placed on the same stigma. 

 I ascertained this by fertilising several flowers, first ille- 

 gitimately, and twenty-four hours afterwards legitimately, 

 with pollen taken from a peculiarly coloured variety, and 

 all the seedlings were similarly coloured; this shows that 

 the legitimate pollen, though applied twenty-four hours sub- 

 sequently, had wholly destroyed or prevented the action of 

 the previously applied illegitimate pollen. Again, as in 

 making reciprocal crosses between the same two species, 

 there is occasionally a great difference in the result, so the 

 same thing occurs with trimorphic plants; for instance, the 

 mid-styled form of Lythrum salicaria was illegitimately fer- 

 tilized with the greatest ease by pollen from the longer sta- 

 mens of the short-styled form, and yielded many seeds ; but 

 the latter form did not yield a single seed when fertilised by 

 the longer stamens of the mid-styled form. 



In all these respects, and in others which might be added, 

 the forms of the same undoubted species when illegitimately 

 united behave in exactly the same manner as do two distinct 

 species when crossed. This led me carefully to observe 

 during four years many seedlings, raised from several illegiti- 

 mate unions. The chief result is that these illegitimate plants, 

 as they may be called, are not fully fertile. It is possible to 

 raise from dimorphic species, both long-styled and short- 

 styled illegitimate plants, and from trimorphic plants all three 

 illegitimate forms. These can then be properly united in a 

 legitimate manner. When this is done, there is no apparent 

 reason why they should not yield as many seeds as did their 

 parents when legitimately fertilised. But such is not the 

 case. They are all infertile, in various degrees ; some being 

 so utterly and incurably sterile that they did not yield dur- 

 ing four seasons a single seed or even seed-capsule. The 

 sterility of these illegitimate plants, when united with each 

 other in a legitimate manner, may be strictly compared with 

 that of hybrids when crossed inter se. If, on the other hand, 

 a hybrid is crossed with either pure parent-species, the steril- 

 ity is usually much lessened; and so it is when an illegitimate 

 plant is fertilised by a legitimate plant. In the same man- 



