CHAP. IX.] AND TBIMOKPHISM. 237 



stigma of a flower, and its own pollen be afterwards, even after 

 a considerable interval of time, placed on the same stigma, its 

 action is so strongly prepotent that it generally annihilates the 

 effect of the foreign pollen ; so it is with the pollen of the several 

 forms of the same species, for legitimate pollen is strongly pre- 

 potent over illegitimate pollen, when both are placed on the same 

 stigma. I ascertained this by fertilising several flowers, first 

 illegitimately, and twenty-four hours afterwards legitimately, with 

 pollen taken from a peculiarly coloured variety, and all the seed- 

 lings were similarly coloured ; this shows that the legitimate 

 pollen, though applied twenty-four hours subsequently, had wholly 

 destroyed or prevented the action of the previously applied ille- 

 gitimate 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 illegiti- 

 mately fertilised 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 fertilised by the 

 longer stamens of the mid -sty led 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 specie* 

 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 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 during 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 sterility is usually 

 much lessened : and so it is when an illegitimate plant is fertilised 

 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 the sterility of 

 certain illegitimate plants was unusually great, whilst 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 





