18 



A SCt.EROTlAL DISEASE OF RlCK. 



of the host (PI. Ill, Fig I), so too much stress must not be laid 

 on this character. The first sclerotia usually occur about the top 

 of the first leaf sheath, either on its inner or outer surface ; in the 

 former case they appear as small dark swellings beneath the dry 

 and withered leaf base. The time taken from the first infection 

 until the death of the plant and the production of the sclerotia is 

 about two weeks. 



Portions of dead Knd dj'ing plants, some of which had not 

 yet produced scleiotia, were incubated in agar tubes. In all 

 cases they gave cultures of Sderotium Oi-yzre, which exactly 

 resembled those from which the inoculations had been made. 

 Since the infections showed that the fungus was strongly 

 parasitic, and could penetrate the uninjured external surface of 

 the plant, it was not considered necessary to make wound inocula- 

 tions. On the whole, 70 — 80% of the inoculations proved fatal. 



Microscopic examination showed that the behaviour of the 

 mvcelinm in the infected culm was not without interest. The 



I>ulk of tlif liypli.i' Hppcar to lun longitudinally in the large air 

 cavities of the leaf and in the cells bordering on them (PI. II, 

 Fig. 11), while a certain number grow outside the leaves in the 

 spaces between the folds of the lamina ; these latter are particu- 

 larly obvious investing the delicate edges of the inner leaf (see 

 text figure). It is nt spf)ts such as this that the rice plant is 



