DETAILED ACCOUNT OF SPECIFIC PLANT DISEASES 



551 



the broken stub of the main root system. Nature attempts to repair 

 the damage in the tobacco by the formation of a cluster of new roots, 

 so that affected plants may not be killed, but remain in the stunted 

 form (Figs. 196 and 197). 



The intercellular mycelium is septate, hyaline at first and consists 

 of narrow hyphae. The fungus produces three kinds of spores, which 



Fig. 196. — -Tobacco roots affected by rot (Thielavia basicola). i, Inoculated at 

 two months; 2, diseased root from field. {After Gilbert, W. W., Bull. 158, U. S. 

 Bureau of Plant Industry, 1909.) 



are according to Duggar (i) endosporous conidia, which are formed in 

 chains in terminal branches, or clusters of branches. They are formed 

 by basipetal septa tion, as short cylindric cells within the branch. 

 The tip of the branch is broken off, and they are pushed out by osmotic 

 force, so that the branch has served as a spore case. The hyaline 



