Chap. IX.] AND TKIMOKPHISM. 31 



longer stamens of the short-styled form, and yielded 

 many seeds ; but the latter form did not yield a single 

 seed when fertilised by the longer stamens of the mid- 

 styled form. 



In all these respects, and in others which might be 

 added, the forms of the same undoubted species when 

 illegitimately united behave in exactly the same 

 manner as do two distinct species when crossed. This 

 led me carefully to observe during four years many 

 seedlings, raised from several illegitimate unions. The 

 chief result is that these illegitimate plants, as they 

 may be called, are not fully fertile. 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 m as did their parents when legiti- 

 mately 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 illegiti- 

 mate plants was unusually great, whilst the sterility of 

 21 



