GENESIS, KEEEDITY, AND VARIATION. 281 



twlls and germ-cells of the same flower, are not quite homo- 

 geneous — if in some of the ovules the physiological units 

 derived from the one parent greatly predominate, and in some 

 of the ovules those derived from the other parent ; and if the 

 like is true of the pollen-cells ; then, some of the ovules may 

 be nearly as much contrasted with some of the pollen-cells, in 

 the characters of their contained units, as were the ovules and 

 poUen-cells of the parents from which the plant proceeded. 

 Between part of the sperm-cells and part of the germ-cells, the 

 community of nature will be such that fertilization wUl not 

 result from their union ; but between some of them, the 

 differences of constitution will be such that their union 

 wiU produce the requisite molecular instability. The facts, 

 so far as they are known, seem in harmony with this deduction. 

 Self-fertilization in flowers, when it takes place, is not so 

 efficient as mutual fertilization. Though some of the ovules 

 produce seeds, yet more of them than usual are abortive. 

 From which, indeed, results the establishment of varieties that 

 have structures favourable to mutual fertilization; since, bein» 

 more proKfic, these have, other things equal, greater chances 

 in the " struggle for existence." 



Further evidence is at hand in support of this interpreta- 

 tion. There is reason to believe that self-fertilization, which 

 at the best is comparatively ineificient, loses aU efficiency in 

 course of time. After giving an account of the provisions for 

 an occasional, or a frequent, or a constant crossing between 

 flowers ; and after quoting Prof. Huxley to the efiect that 

 among hermaphrodite animals, there is no case in which " the 

 occasional influence of a distinct individual can be shown to 

 bo physically impossible ; " Mr Darwin writes — " from these 

 several considerations and from the many special facts which 

 I have collected, but which I am not here able to give, I am 

 *strongly inclined to suspect that, both in the vegetable and 

 animal kingdoms, an occasional intercross with a distinct in- 

 dividual is a law of nature. * * * in none, as I susjject, 

 can self-fertilization go on for perpetuity." This conclusion, 

 19 



