CHAP. IX. SELF-STERILE PLANTS. 343 



the stigma deeply ;* and with the Orchidaceous genus 

 Notylia they failed altogether to penetrate it. 



With dimorphic and trimorphic species, an illegiti- 

 mate union between plants of the same form presents 

 a close analogy with self-fertilisation, whilst a legi- 

 timate union closely resembles cross-fertilisation ; and 

 here again the lessened fertility or complete sterility of 

 an illegitimate union depends, at least in part, on the 

 incapacity for interaction between the pollen-grains 

 and stigma. Thus with Linum grandiflorum, as I 

 have elsewhere shown,f not more than two or three 

 out of hundreds of pollen-grains, either of the long- 

 styled or short-styled form, when placed on the 

 stigma of their own form, emit their tubes, and 

 these do not penetrate deeply; nor does the stigma 

 itself change colour, as occurs when it is legitimately 

 fertilised. 



On the other hand the difference in innate fertility, 

 as well as in growth between plants raised from crossed 

 and self-fertilised seeds, and the difference in fertility 

 and growth between the legitimate and illegitimate 

 offspring of dimorphic and trimorphic plants, must 

 depend on some incompatibility between the sexual 

 elements contained within the pollen-grains and ovules, 

 as it is through their union that new organisms are 

 developed. 



If we now turn to the more immediate cause of 

 self-sterility, we clearly see that in most cases it is de- 

 termined by the conditions to which the plants have 

 been subjected. Thus Eschscholtzia is completely self- 

 sterile in the hot climate of Brazil, but is perfectly 

 fertile there with the pollen of any other individual. 

 The offspring of Brazilian plants became in England 



* <Bot. Zeitung,'1868,pp.ll4, t 'The Different Forma of 

 115. Flowers,' &c., p. 87 



