168 HYBRIDISM. Chap. XIX. 



whether they were specifically distinct. He would find that 

 they yielded only about one-fifth of the proper number of 

 seed, and that they behaved in all the other above-specified 

 respects as if they had been two distinct species. But to 

 make the case sure, he would raise plants from his supposed 

 hybridised seed, and he would find that the seedlings were 

 miserably dwarfed and utterly sterile, and that they behaved 

 in all other respects like ordinary hybrids. He might then 

 maintain that he had actually proved, in accordance with the 

 common view, that his two varieties were as good and as 

 distinct species as any in the world ; but he would be com- 

 pletely mistaken. 



The facts now given on dimorphic and trimorphic plants 

 are important, because they show us, first, that the physio- 

 logical test cf lessened fertility, both in first crosses and in 

 hybrids, is no criterion of specific distinction ; secondly, 

 because we may conclude that there is some unknown bond 

 which connects the infertility of illegitimate unions with that 

 of their illegitimate offspring, and we are led to extend the 

 same view to first crosses and hybrids ; thirdly, because we 

 find, and this seems to me of especial importance, that two or 

 three forms of the same species may exist and may differ in no 

 respect whatever, either in structure or in constitution, 

 relatively to external conditions, and yet be sterile when 

 united in certain ways. For we must remember that it is 

 the union of the sexual elements of individuals of the same 

 form, for instance, of two long-styled forms, which results in 

 sterility ; whilst it is the union of the sexual element proper 

 to two distinct forms which is fertile. Hence the case appears 

 at first sight exactly the reverse of what occurs in the 

 ordinary unions of the individuals of the same species, and 

 with crosses between distinct species. It is, however, doubt- 

 ful whether this is really so ; but I will not enlarge on this 

 obscure subject. 



We may, however, infer as probable from the consideration 

 of dimorphic and trimoiphic plants, that the sterility of dis- 

 tinct species when crossed, and of their hybrid progeny, 

 depends exclusively on the nature of their sexual elements, 

 and not on any difference in their structure or general con- 



