GROWTH AND REPRODUCTION. 2 25 



of nutrition and crises of reproduction, hunger and love, 

 must be interpreted as life-tides, ^vhich will be seen to be but 

 special expressions of- the fundamental organic rhythai between 

 sleep and waking, rest and work, upbuilding and expenditure, 

 which are expressed on the protoplasmic plane as anabolism 

 and katabolism. 



The common hydra, in abundant nutritive conditions, 

 produces numerous buds, and even these sometimes begin 

 themselves to bear another generation. In other words, we 

 may almost say, with plenty of food the polypegroias abundantly, 

 so obviously is this asexual reproduction continuous with growth. 

 A check to the nutritive conditions, however, brings on the de- 

 velopment of the sexual organs and the occurrence of sexual 

 reproduction. In planarian worms, the asexual multiplication 

 of which we have already noted, Zacharias observed that 

 favourable nutritive conditions were associated with the forma- 

 tion of asexual chains, while a check to the nutrition brought 

 about both the separation and the sexual maturity of the links. 

 Rywosch corroborates this, noting in Microstoinum lineare that 

 the generative organs do not become completely matured till 

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

 sexuality is hastened by outside influences such as checked 

 nutrition. The gardener root-prunes his apple-tree, thereby 

 checking nutrition to improve the yield of fruit, in other words, 

 to augment reproduction. Reversely, the removal of repro- 

 ductive organs may increase the development of the general 

 " body " both in plant and animal, — witness the castrated ox, 

 capon, &c., or the way in which the gardener nips off the flower- 

 buds from his foliage plants. Taking a further step, we recall 

 the familiar and already repeated fact, that favourable nutritive 

 and other conditions enable the aphides to continue partheno- 

 genetic through the summer months ; but both for the common 

 plant-lice and for the vine-insect phylloxera, it has been shown 

 that a check to nutrition causes the parthenogenesis to cease, 

 and is associated with the return of sexual reproduction. The 

 above instances are obviously not all upon the same plane. 

 They illustrate however, at different levels, the same great con- 

 trast. It is necessary, however, to become more precise. 



i^ 6. The Contrast between Gjvwth and Repi'oduction in the 

 Individual. — {ci) The Distribution of Organs. — The general 

 position of the flow'er at the end of the vegetative axis is so 

 obvious a fact that its import tends to be overlooked. The end 



p 



