Chap. V. HETEEOSTYLED PLANTS. 241 



sterile. But there are marked exceptions, as shown 

 by Gartner, to these rules. So it is with illegitimate 

 unions and illegitimate oifspring. Thus the mid- 

 styled form of Lythrum salicaria, when illegitimately 

 fertilised with pollen from the longest stamens of 

 the short-styled form, produced an unusual number 

 of seeds ; and their illegitimate offspring were not at 

 all, or hardly at all, sterile. On the other hand, the 

 illegitimate offspring from the long-styled form, ferti- 

 lised with pollen from the shortest stamens of the same 

 form, yielded few seeds, and the illegitimate offspring 

 thus produced were very sterile ; but they were more 

 sterile than might have been expected relatively to the 

 difficulty of effecting the union of the parent sexual 

 elements. No point is more remarkable in regard to 

 the crossing of species than their unequal reciprocity. 

 Thus species A will fertilise B with the greatest ease ; 

 but B will not fertilise A after hundreds of trials. We 

 have exactly the same case with illegitimate unions ; 

 for the mid-styled Lythrum salicaria was easily ferti- 

 lised by pollen from the longest stamens of the short- 

 styled form, and yielded many seeds ; but the latter 

 form did not yield a single seed when fertilised by the 

 longest stamens of the mid-styled form. 



Another important point is prepotency. Gartner 

 has shown that when a species is fertilised with pollen 

 from another species, if it be afterwards fertilised with 

 -its own pollen, or with that of the same species, this 

 is so prepotent over the foreign pollen that the effect 

 of the latter, though placed on the stigma some time 

 previously, is entirely destroyed. Exactly the same 

 thing occurs with the two forms of a heterostyled 

 species. Thus several long-styled flowers of Primula 

 veris were fertilised illegitimately with pollen from 

 another plant of the same form, and twenty-four hours 



