294 THE CELL 



Infusoria, which are approaching sexual maturity, may be induced 

 to pair by withholding nourishment. " Une riche alimentation," 

 as Maupas observes, " endort l'appetit conjugant; le jeune, au 

 contraire, l'eveille et l'excite." 



Similarly Klebs (VII. 28) has observed in Hydrodictyon, that 

 changes in the environment influence the development of sexual 

 cells, by either inducing or hindering the process. 



Klebs has induced the formation of gametes in " nets," which 

 were growing naturally, by cultivating them in a 7 to 10 per cent, 

 solution of cane sugar. After from five to ten days, the net fell 

 completely to pieces, gametes having developed in nearly all the 

 cells. Further, the inclination for the formation of gametes was 

 increased in the cells by cultivating fresh nets in shallow glass 

 dishes, which contained a relatively small quantity of water, and 

 which were placed in a sunshiny window. According to Klebs, 

 the influence of chamber culture is " to arrest growth, but not to 

 interfere with the production of organic compounds by means of 

 assimilation ; at the same time, however, a certain poorness in 

 nutrient salts is produced." 



On the other hand, sexual reproduction may be suppressed, as 

 in Ciliata. For this purpose it is only necessary to place a net, 

 the cells of which have just commenced to form gametes, in a 5 

 to 1 per cent, nutrient solution composed of 1 part sulphate of 

 magnesia, 1 part phosphate of potassium, 1 part sulphate of potas- 

 sium, and 4 parts sulphate of calcium. After a short time, asexual 

 swarm-spores develop, especially if the net is put back into fresh 

 water. 



Eidam has observed that a small fungus, Basidiobolus ranarum, 

 when cultivated from conidia in a nutrient medium, develops a 

 firm mycelium, which produces simultaneously both asexual re- 

 productive cells (conidia) and sexual cells. In an exhausted 

 nutrient medium, on the contrary, the conidia produce only a 

 loose mycelium, which immediately and exclusively gives rise to 

 sexual cells, which unite together to form zygospores. 



Abundant nourishment in plants is conducive to vegetative in- 

 crease, as the experience of gardeners teaches us, but hinders the 

 formation of seed, whereas the development both of bloom and 

 seed is increased by restricting vegetative growth (cutting off 

 roots and shoots), and thus diminishing the absorption of nourish- 

 ment. 



The same phenomenon has also been observed in animals, which 



