ASEXUAL GENESIS AND OVULATION 149 



tion of the food at once reintroduce males and sexual 

 reproduction." l 



It is impossible to cover these facts by a single 

 formula, as Herbert Spencer tried to do, assuming that 

 the two forms of reproduction react in the same manner to 

 the same conditions. As a matter of fact, they appear 

 in most cases under diametrically opposite conditions. 

 Spencer has himself admitted that it is impolitic to dung 

 the roots of fruit-trees while the growth of sexless axes 

 is still abundant, this growth being merely a form of 

 asexual reproduction, and a sign that the tree is in too 

 high a state of nutrition to produce fruit ; whilst Darwin 

 mentions that in order to make European vegetables in 

 India yield seed, it is necessary to take them up and cut 

 or mutilate their tap-roots, obviously for the purpose of 

 checking nutrition. 



The term " discontinuous growth " has little application 

 to sexual reproduction, but it may fairly be applied to 

 the asexual process. " The common hydra, in abundant 

 nutritive conditions, produces numerous buds, and even 

 these sometimes begin themselves to produce another 

 generation. In other words, we may almost say, with 

 plenty of food the polype grows abundantly, so obviously 

 is this asexual reproduction continuous with growth. 

 A check to the nutritive conditions, however, brings 

 on the development of the sexual organs and the occur- 

 rence of sexual reproduction. In planarian worms . . . 

 Zacharias observed that favourable nutritive conditions 

 were associated with the formation of asexual chains, 

 while a check to the nutrition brought about both the 

 separation and sexual maturity of the links. Bywosch 

 corroborates this, noting in Microstomum lineare that 

 the generative organs do not become completely matured 

 till the individuals cease to be links in a chain, and that 

 1 Evolution of Sex, Geddes and Thomson, chap. iv. 



