30 HETKEOSTYLED DIMOEPHIC PLANTS. Chap. I. 



legitimate and illegitimate unions of Primula. With 

 P. veris, for every 100 seeds yielded by the two le- 

 gitimate unions, only 64 were yielded by an equal 

 number of good capsules from the two illegitimate 

 unions. With P. Sinensis, as we shall hereafter see, 

 the proportion was nearly the same — namely, as 100 

 to 62. Now Gartner has shown that, on the calcula- 

 tion of Verhascum lychnitis yielding with its own pollen 

 100 seeds, it yielded when fertilised by the pollen of 

 V. Phceniceum 90 seeds ; by the pollen of V. nigrum, 

 63 seeds ; by that of V. Uattaria, 62 seeds. So again, 

 Bianihus barbatus fertilised by the pollen of D. superbus 

 yielded 81 seeds, and by the pollen of D. Japonicus 

 66 seeds, relatively to the 100 seeds produced by its 

 own pollen. We thus see — and the fact is highly re- 

 markable — that with Primula the illegitimate unions 

 relatively to the legitimate are more sterile than 

 crosses between distinct species of other genera rela- 

 tively to their pure unions. Mr. Scott has given* a 

 still more striking illustration of the same fact : he 

 crossed Primula auricula with pollen of four other 

 species (P. Palinuri, viscosa, hirsuta, and verticiUatd), 

 and these hybrid unions yielded a larger average 

 number of seeds than did P. auricula when fertilised 

 illegitimately with its own-form pollen. 



The benefit which heterostyled dimorphic plants de- 

 rive from the existence of the two forms is sufficiently 

 obvious, namely, the intercrossing of distinct plants 

 being thus ensured.t Nothing can be better adapted 

 for this end than the relative positions of the anthers 

 and stigmas in the two forms, as sliown in Fig. 2 ; but to 



• ' Journ. Linn. Soo. Bol.,' vol. fertilisation ' how greatly the ofF- 



viii. 1864, p. 93. spring from intercrossed plants 



t I have shown in my work profit in height, vigour, and 



on tlio ' Effects of Cross and Solf- fertility. 



