Chap. XIX. HYBRIDISM. 183 



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 steri- 

 lity of the union from which they were derived was by no means 

 great. With hybrids raised from the same seed-capsule the 

 degree of sterility is innately variable, so it is in a marked 

 manner with illegitimate plants. Lastly, many hybrids are 

 profuse and persistent flowerers, whilst 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 beha- 

 viour between illegitimate plants and hybrids. It is hardly an 

 exaggeration to maintain that the former are hybrids, but pro- 

 duced within the limits of the same species by the improper 

 union of certain forms, whilst ordinary hybrids are produced 

 from an improper union between so-called distinct species. We 

 have already seen that there is the closest similarity in all re- 

 spects between 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 Lytlirum 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 

 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 



