GRO WTH. 



119 



sion, thus drawing water forcibly through the protoplasmic mem- 

 brane. Since it does not filter out readily, the increase in 



tig. log. 

 Spores of mucor, and different stages ot germiDation. 



quantity of the water in the cell piroduces a pressure from within 

 which stretches the membrane, and the ela,stic cell wall )ields. 

 Thus the gonidium becomes larger. 



243. How the gonidia germinate. — "We should find at this 

 time many of tlie gonidia extended on one side into a tube-like 

 process the length of wliich varies according to time and tempera- 

 ture. The short process thus begun continues to elongate. This 

 elongation of the plant is growth, or, more properly speaking, one 

 of the phenomena of growth. 



244. The germ tube branches and forms the mycelium. — 

 In the course of a day or so branches from the tube will appear. 

 This branched form of the threads of the fungus is, as we 

 remember, the mvcelium. We can still see the point where 

 growth started from the gonidium. Perhaps by this time se\"eral 

 tubes have grown from a single one. The threads of the m\ ce- 

 lium near the gonidium, that is, the older portions of them, have 

 increased in diameter as they have elongated, though this increase 

 in diameter is by no means so great as the in( rease in length. 

 After increasing to a certain extent in diameter, growth in this 

 direction ceases, while apical growth is practically unlimited, 

 being limited only by the supply of nutriment. 



245. Growtb in length takes place only at the end of the 

 thread. — If there were an) Ijranches on the mycelium when the 



