30 HETEROSTYLBD DIMORPHIC PLANTS. Chap. I. 



the proportion was nearly the same — namely, as 100 

 to 63. 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. Phomiceum 90 seeds; by the pollen of V. nigrum, 

 63 seeds; by that of V. hlattaria, 63 seeds. So again, 

 Dianthus barbatits fertilised by the pollen of D. superbus 

 yielded 81 seeds and by the pollen of D. Japonicus 

 I 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 illusti;ation of the same fact: he 

 crossed Primula auricula with pollen of four other 

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

 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. 3 ; 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 



* 'Jounj. titm. Soo. Bot.,' vol. fertilisation' how greatly the off- 



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



f I have shown in my work on profit in height, vigour, and fer- 



the 'Effects of Cross arid Self- tUity. 



