CHAP. IX. AND SELF-FERTILISED PLANTS. 313 



in the second place, the fertility of its hybrid off- 

 spring. Thes-j two classes of cases do not always run 

 parallel ; thus some plants, as Gartner has shown, can 

 be crossed with great ease, but yield excessively sterile 

 hybrids ; while others are crossed with extreme diffi- 

 culty, but yield fairly fertile hybrids. 



The natural order to follow in this chapter would 

 have been first to consider the effects on the fertility 

 of the parent-plants of crossing them, and of fertilising 

 them with their own pollen ; but as we have discussed 

 in the two last chapters the relative height, weight, 

 and constitutional vigour of crossed and self-fertilised 

 plants that is, of plants raised from crossed and 

 self-fertilised seeds it will be convenient here first 

 to consider their relative fertility. The cases observed 

 by me are given in the following table, D, in which 

 plants of crossed and self-fertilised parentage were left 

 to fertilise themselves, being either crossed by insects 

 or spontaneously self-fertilised. It should be observed 

 that the results cannot be considered as fully trust- 

 worthy, for the fertility of a plant is a most variable 

 element, depending on its age, health, nature of the 

 soil, amount of water given, and temperature to which 

 it is exposed. The number of the capsules produced 

 and the number of the contained seeds, ought to have 

 been ascertained on a large number of crossed and self- 

 fertilised plants of the same age and treated in every 

 respect alike. In these two latter respects my observa- 

 tions may be trusted, but a sufficient number of capsules 

 were counted only in a few instances. The fertility, 

 or- as it may perhaps better be called the productive- 

 ness, of a plant depends on the number of capsules 

 produced, and on the number of seeds which these 

 contain. But from various causes, chiefly from the 

 want of time, I was often compelled to rely on the 



