GENESIS, HEREDITY, AND VARIATION. 343 



germ-cells produced by such an organism must, in virtue of 

 these same laws, be more or less unlike one another. It wa-o 

 shown that through segregation, some of the sperm-cells or 

 germ-cells will get an excess of the physiological units derived 

 from one side, and some of them an excess of those derived 

 from the other side: a cause which accounts for the unlike- 

 nesses among offspring simultaneously produced. N'ow from 

 this segregation of the different orders of physiological units, 

 inherited from different parents and lines of ancestry, there 

 arises the possibility of self-fertilization in hermaphrodite 

 organisms. If the physiological units contained in the sperm- 

 cells 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 

 pollen-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 will 

 not result from their union; but between some of them, 

 the differences of constitution will be such that their union 

 will produce the requisite molecular instability. The facts, 

 so far as they are known, seem in harmony with this deduc- 

 tion. 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 abor- 

 tive. From which, indeed, results the establishment of varie- 

 ties that have structures favourable to mutual fertilization; 

 since, being more prolific, these have, other things equal, 

 greater chances in the " struggle for existence." 



Further evidence is at hand supporting this interpreta- 

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

 at the best is comparatively inefficient, loses all efficiency in 



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

 23 



