or 

 to 



436 MR. C. DAEWIN ON DIMOKPHIC AKB TllIMORPHlC PLAINTS, 



ing in seedlings of the same parentage, and being much aiFected 

 by the nature of the conditions ; the more sterile plants being 

 dwarfed in stature, weakly in constitution, and liable to premature 

 death ; the anthers being often contabescent ; the first unions and 

 the offspring being generally sterile in a parallel degree, but with 

 marked exceptions to the rule ; the fertility of the offspring being 

 increased by a cross with a legitimate form, or with one of the pure 

 parent forms ; the unequal reciprocity in sexual power between 

 the same two forms or between the same two species ; and, lastly, 

 the prepotent action of legitimate pollen in the one case, and of 

 the plant's own pollen In the other case. Hence it is hardly an 

 exaggeration to assert that the illegitimate offspring from an ille- 

 gitimate union are hybrids formed within the limits of one and 

 the same species. 



This conclusion is Important ; for, as I have elsewhere * more 

 fully explained, Ave thus learn, first, that the lessened fertility of 

 tlie first union and of the offspring of two forms is uo sure criterioji 

 of specific distinctness. If any one were to cross two varieties of 

 the same form of Lythrum or Primula for the sake of ascertainin 

 whether they were specifically distinct, and he found that they and 

 their offspring were extremely sterile, and that they resembled in a 

 whole series of relations crossed species and their hybrid offspring, 

 he would maintain that his varieties had been proved to be good 

 and true t^pecles ; but he would be completely deceived. In the 



r 



second place, as the forms of the same trimorphic or dimorphic 

 species are obviously identical, with the exception of the repro- 

 ductive organs, in general structure, and as ihey are identical in 

 general constitution (for they live under precisely the same con- 

 ditions), the sterility of their illegitimate unions, and that of their 

 illegitimate ofi'sprlng, must depend exclusively on the nature of 

 the sexual elements and on their incompatibility for uniting in a 

 particular manner. And as we have just seen that distinct 

 species wben crossed resemble in a whole series of relations the 

 forms of the same species when Illegitimately united, we are 

 led to conclude that in this case likewise the sterility de- 

 pends exclusively on the incompatible nature of their sexual 

 elements, and not on any general difference in constitution or 

 structure. We are, indeed, led to this same conclusion by the 

 impossibility of detecting any difference suflScient to account for 

 certain species crossing with the greatest ease, whilst other closely 



* Origin of Species*. 4th edit. 1866, p. o2o. Variation of Animals kc. under 

 Domcsticatinn, 1868, toI. ii. p. 184. 



