ASEXUAL GENESIS AND OVULATION 151 



be no reproduction. From this point upwards sexual 

 reproduction becomes more and more possible as con- 

 ditions improve up to a certain point, the optimum or 

 best point for fertility. After that point has been passed, 

 sexual reproduction becomes less and less possible as 

 vitality expands under the influence of increasingly favour- 

 able conditions, until complete sexual sterility is produced. 

 But the conditions which are inimical to sexual repro- 

 duction are favourable to the asexual process, and as 

 conditions become steadily less favourable to the former, 

 they become steadily more favourable to the latter. 



Taking the line from the other end we see that extremely 

 favourable nutritive conditions cause sexual sterility, but 

 favour the asexual method of reproduction, as in a fruit- 

 tree which is sterile sexually and bears no fruit owing 

 to the fact that it is running to shoots and foliage through 

 being too heavily manured. But the check to nutrition 

 decreases the amount of asexual reproduction and renders 

 the sexual process and the production of fruit possible. 

 The degree of sexual fertility increases and the degree of 

 asexual fertility decreases until the optimum point for 

 sexual fertility is reached. After that both sexual and 

 asexual fertility diminish until starvation point is reached. 

 Of course, there is no clean-cut division in the nutritive 

 scale where one process ends and the other begins. The 

 two processes may often be seen going on together. But 

 that in no way affects the general principle. 



The two methods of reproduction are parts of a coherent 

 scheme, and, apart from instinct as a regulating factor, 

 the above diagram illustrates the whole plan of the 

 reaction of the degree of fertility to the action of the 

 environment. The asexual process is the predominant 

 method of reproduction among the lower forms of life, 

 being eminently adapted to the peculiar conditions of 

 their environment, and enabling them to multiply with 



