254 RECIPROCAL DIMORPHISM [Chap. IX 



that these illegitimate plants, as they may be called, are not fully fer- 

 tile. It is possible to raise from dimorphic species, both long-styled 

 and short-styled illegitimate plants, and from trimorphic plants all 

 three illegitimate forms. These 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 

 legitimately fertilised. But such is not the case. They are all 

 infertile, 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. The sterility of these illegitimate plants, when 

 united with each other in a legitimate manner, may be strictly 

 compared with that of hybrids when crossed inter se. If, 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 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 behaviour 

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

 ration to maintain that illegitimate plants are hybrids, produced 

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

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

 proper 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 

 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 hybridised seed, and he would 



