312 FERTILITY OF CROSSED CHAP. IX. 



CHAPTER IX. 



THE EFFECTS OF CROSS-FEBTILISATION AND SELF-FERTILISATION OK 

 THE PRODUCTION OF SEEDS. 



Fertility of plants of crossed and self-fertilised parentage, both lota 

 being fertilised in the same manner Fertility of the parent-plants 

 when first crossed and self-fertilised, and of their crossed and self- 

 fertilised offspring when again crossed and self-fertilised Com- 

 parison of the fertility of flowers fertilised with their own pollen 

 and with that from other flowers on the same plant Self-sterile 

 plants Causes of self-sterility The appearance of highly self- 

 fertile varieties Self-fertilisation apparently in some respects bene- 

 ficial, independently of the assured production of seeds. Kelative 

 weights and rates of germination of seeds from crossed and telf- 

 fertilised flowers. 



THE present chapter is devoted to the Fertility of 

 plants, as influenced by cross-fertilisation and self- 

 fertilisation. The subject consists of two distinct 

 branches ; firstly, the relative productiveness or fertility 

 of flowers crossed with pollen from a distinct plant and 

 with their own pollen, as shown by the proportional 

 number of capsules which they produce, together 

 with the number of the contained seeds. Secondly, 

 the degree of innate fertility or sterility of the seed- 

 lings raised from crossed and self-fertilised seeds ; such 

 seedlings being of the same age, grown under the same 

 conditions, and fertilised in the same manner. These 

 two branches of the subject correspond with the two 

 which have to be considered by any one treating of 

 hybrid plants; namely, in the first place the comparative 

 productiveness of a species when fertilised with pollen 

 from a distinct species and with its own pollen ; and 



