Chap. XIX. HYBRIDISM. 167 



can then be properly united in a legitimate manner. When 

 this is done, there is no apparent reason why they should 

 not yield as many seeds as did their parents when legiti- 

 mately fertilised. But such is not the case ; they are all 

 infertile, but in various degrees ; some being so utterly and 

 incurably sterile that they did not yield during four seasons 

 a single seed or even seed-capsule. These illegitimate plants, 

 which are so sterile, although united with each other in a 

 legitimate manner, may be strictly compared with hybrids 

 when crossed inter se, and it is well known how sterile these 

 latter generally are. When, on the other hand, a hybrid is 

 crossed 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 sterility 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 illegiti- 

 mate 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. 



Although there is the closest identity in character and 

 behaviour between illegitimate plants and hybrids, it is 

 hardly an exaggeration to maintain that the former are 

 hybrids, but produced 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 respects 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 

 Ly thrum salicaria, and that he determined to try by crossing 



