HYBRIDISM 259 



plants. Lastly, many hybrids are profuse and persistent flowerers, 

 while other and more sterile hybrids produce few flowers, and are 

 weak, miserable dwarfs; exactly similar cases occur with the 

 illegitimate offspring of various dimorphic and trimorphic plants. 



Altogether there is the closest identity in character and behavior 

 between illegitimate plants and hybrids. It is hardly an exaggera- 

 tion to maintain that illegitimate plants are hybrids, produced 

 within the limits of the same species by the improper union of 

 certain forms, while ordinary hybrids are produced from an im- 

 proper union between so-called distinct species. We have also al- 

 ready seen that there is the closest similarity in all respects be- 

 tween first illegitimate unions and first crosses between distinct 

 species. This will perhaps be made more fully apparent by an 

 illustration; we may suppose that a botanist found two well- 

 marked varieties (and such occur) of the long-styled form of 

 the trimorphic Lythrum salicaria, and that he determined to 

 try by crossing 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 hybridized 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 vari- 

 eties were as good and as distinct species as any in the world; but 

 he would be completely mistaken. 



The facts now given on dimorphic and trimorphic plants are 

 important, because they show us, first, that the physiological test 

 of lessened fertility, both in first crosses and in hybrids, is no safe 

 criterion of specific distinction; secondly, because we may con- 

 clude that there is some unknown bond which connects the in- 

 fertility of illegitimate unions with that of their illegitimate off- 

 spring, and we are led to extend the same view to first crosses and 

 hybrids; thirdly, because we find, and this seems to me of es- 

 pecial importance, that two or three forms of the same species 

 may exist and may differ in no respect whatever, either in struc- 

 ture 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; while it is the union of the sexual elements proper 

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



