300 RECIPROCAL DIMORPHISM 



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 indentity in character and 

 behavior between illegitimate plants and hybrids. It is 

 hardly an exaggeration 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 improper union between so- 

 called distinct species. We have also already seen that 

 there is the closest similarity in all respects between first 

 illegitimate unions and first crosses between distinct species. 

 This will perhaps be made more fully apparent by an illus* 

 tration; 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 deter- 

 mined 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 com- 

 mon view, that his two varieties were as good and as dis- 

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

 pletely mistaken. 



The facts now given ondimorj^hic and trimorphic plants 

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

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

 hybrids, is no safe 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 impor- 

 tance, 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 con' 



