



30 



HETEROSTYLED DIMORPHIC PLANTS. Chap. I. 



the proportion was nearly the same — namely, as 100 

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

 tion of Verbascum lynchnitis yielding with its own pol- 

 len 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. blattaria, 62 seeds. So again, 

 Dianthus 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 v erticillata) , 

 and these hybrid unions yielded a larger average num- 

 ber of seeds than did P. auricula when fertilised illegiti- 

 mately 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, f Nothing can be better adapted 

 for this end than the relative positions of the anthers 

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

 this whole subject I shall recur. No doubt pollen will 

 occasionally be placed by insects or fall on the stigma 

 of the same flower; and if cross-fertilisation fails, such 

 self-fertilisation will be advantageous to the plant, as 

 it will thus be saved from complete barrenness. But 

 the advantage is not so great as might at first be 















* ' Jonrn. Linn. Soc. Bot.,' vol. 

 viii., 1864, p. 93. 



} I have shown in my work on 

 the * Effects of Cross and Self- 



fertilisation ' how greatly the off- 

 spring from intercrossed plants 

 profit in height, vigour, and fer- 

 tility. 









