110 



As regards sexual reproduction, it is clear that in an herma- 

 phrodite flower it is possible (1) for the pistil to be fertilised with 

 pollen developed in the same flower, in which case the flower 

 is said to be self -fertilised and (2) for the pistil to be fertilised by 

 pollen developed in another flower occurring on the same plant 

 or in a flower belonging to a separate plant, in which case the 

 flower is said to be cross-fertilised. Now, a young plant 

 arising from a seed resulting from the second kind of 

 cross-fertilisation must inherit something from each of its 

 parents, and it therefore tends to vary and to exhibit 

 characters which were not found in the mother-plant. It 

 appears that this tendency to differ from the mother-plant also 

 exists to a certain extent in plants arising from seed produced by 

 self -fertilisation, and all plants raised from seed tend to differ 

 more or less considerably from the mother-plant. In asexual 

 reproduction this is not the case and the young plants are 

 invariably found to resemble their mother-plant very closely. 

 In the case of the young plants arising from seed, a large pro- 

 portion of which frequently find themselves at a long distance 

 from their mother and exposed to conditions of existence more 

 or less fundamentally different from those under which their 

 mother-plant developed, the possession of slightly different 

 characteristics may obviously be of the utmost use in enabling 

 them to develop successfully. On the other hand considerable 

 variation in the case of asexually produced offspring, established 

 in the immediate neighbourhood of their parent, would as a rule 

 be a disadvantage. 



98. As regards the respective 



Seif-Fertiiisa- advantages of cross and self-fertilisation, it has been 

 tion. proved by actual experiment in the case of several plants in 



Europe that cross-fertilisation results in the production of 

 more seeds, which in their turn are able to produce more 

 vigorous plants, than is the case with self-fertilisation. Even 

 if this were universally the case, which has not been proved, 

 it must always be remembered that cross-fertilisation is effected 

 with considerable difficulty and is therefore far more uncertain 

 than self-fertilisation, inasmuch as fewer flowers are likely to be 

 fertilised. It would therefore be quite possible for a plant 

 which uniformly produces a large number of young plants as 

 the result of self -fertilisation to be equally, even if not more, 

 successful in the struggle for existence, in comparison with a 

 plant which habitually produces very few offspring as the result 

 of cross-fertilisation, even if the offspring of the latter were 

 slightly more vigorous than those of the former. It is in fact 



