CHAP. IX. SELF-FERTILE VARIETIES. 351 



rule very small compared with that from a cross with 

 a distinct plant. Thus we have seen in the last chapter 

 that seedlings of Ipomcea and Mimulus raised from 

 flowers fertilised with their own pollen, which is the 

 strictest possible form of self-fertilisation, were superior 

 in height, weight, and in early flowering to the seedlings 

 raised from flowers crossed with pollen from other flowers 

 on the same plant ; and this superiority apparently was 

 too strongly marked to be accidental. Again, the cul- 

 tivated varieties of the common pea are highly self- 

 fertile, although they have been self-fertilised for many 

 generations; and they exceeded in height seedlings 

 from a cross between two plants belonging to the same 

 variety in the ratio of 115 to 100 ; but then only four 

 pairs of plants were measured and compared. The 

 self-fertility of Primula veris increased after several 

 generations of illegitimate fertilisation, which is a 

 process analogous to self-fertilisation, but only as long 

 as the plants were cultivated under the same favour- 

 able conditions. I have also elsewhere- shown* that 

 with several species of Primula equal-styled varieties 

 occasionally appear which possess the sexual organs 

 of the two forms combined in the same flower. Con- 

 sequently they fertilise themselves in a legitimate 

 manner and are highly self-fertile ; but the remarkable 

 fact is that they are rather more fertile than ordinary 

 plants of the same species legitimately fertilised by 

 pollen from a distinct individual. Formerly it appeared 

 to me probable, that the increased fertility of these 

 heterostyled plants might be accounted for by the 

 stigma lying so close to the anthers that it was im 

 pregnated at the most favourable age and time of 

 the day ; but this explanation is not applicable to the 



* 'Different Forms of Flower*' &o., p. 272. 



