102 DISEASES OF TROPICAL PLANTS CH. 



causes the least loss. The dead top of the plant may 

 present the most varied appearance, according to the 

 weather conditions and the length of time that it is 

 exposed to the weather, and to the growth of saprophytic 

 organisms. It may appear bleached, blackened, dis- 

 coloured in various ways, or merely withered. Below 

 the lowest affected node the plant is healthy, and 

 abundant normal suckers are put up from the roots. 



Commonly also the leaves are similarly invaded by 

 the fungus at the point where the leaf-blade joins the 

 sheath, and the blades break off. In America the leaf- 

 blades themselves are less frequently affected, but in 

 Japan, Italy, and Kussia this appears to be a serious 

 form of the disease. The writer has seen but one serious 

 outbreak of the leaf-spot form of the disease ; this was 

 in South Carolina, in June, on rice about two feet high. 

 Ordinarily the leaf-spots are not definite in appearance 

 or size, but appear as irregular, often confluent, dead 

 patches ; but fairly discreet, black-margined, or zonated 

 spots are also sometimes seen, resembling quite strongly 

 the Piricularia spots on grasses of the genus Panicuw. 

 The fungus occasionally produces its lesions on the leaf- 

 sheaths and internodes, often following a wound, and 

 very commonly occurs, in late attacks, on the rhachis 

 and pedicels of the head, and even on the glumes of the 

 grains. Finally, the fungus readily attacks the seedling, 

 girdling it at the point where it emerges from the seed. 

 Probably this is the cause of much greater loss than is 

 realized ; and many a failure of stand is undoubtedly 

 due to this, rather than to poor seed or bad water. 



The Fungus. It will thus be seen that the 

 symptoms of the disease are neither conspicuous nor 

 characteristic ; indeed the only dependable diagnostic 

 symptom is the presence of the mycelium. Where the 

 spores can be found at all on the surface of any diseased 

 spot, they are both numerous and conspicuous, but 

 being fugacious in any case, they are often hard to find. 

 If a diseased portion of the plant is placed in slightly 

 damp air (e.g. in a petri dish with a single layer of damp 



