258 THE ORIGIN OF SPECIES 



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 

 fertilizing several flowers, first illegitimately and twenty-four 

 hours afterward legitimately, with pollen taken from a peculiarly 

 colored variety, and all the seedlings were similarly colored; tljis 

 shows that the legitimate pollen, though applied twenty-four hours 

 subsequently, had wholly destroyed or prevented the action of the 

 previously applied illegitimate pollen. Again, as in making re- 

 ciprocal 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 fertilized with the greatest ease by 

 pollen from the longer stamens of the short-styled form, and 

 yielded many seeds; but the latter form did not yield a single 

 seed when fertilized 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 illegitimate 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 fertilized. 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 during 

 four seasons a single seed or even seed-capsule. The sterility of 

 these illegitimate plants, when united with each other in a legiti- 

 mate 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 sterility is usually much 

 lessened and so it is when an illegitimate plant is fertilized by a 

 legitimate plant. In the same manner as the sterility of hybrids 

 does not always run parallel with the difficulty of making the first 

 cross between the two parent-species, so that sterility of certain 

 illegitimate plants was unusually great, while the sterility of the 

 union from which they were derived was by no means great. With 

 hybrids raised from the same seed-capsule the degree of sterility 

 is innately variable, so it is in a marked manner with illegitimate 



