290 DISEASES OF CROP-PLANTS 



to the fact of the invariable association with it of the myceHa of 

 certain fungi which frequently become conspicuously developed 

 on the affected stools. The presence of these fungi is not in 

 itself sufficient to produce any notable effect on the health of 

 the plant, for with the system of cultivation followed in localities 

 favourable to the cane they occur in some abundance in fields 

 bearing good crops, and it is certain that they are present to 

 some extent, though it ma}^ be in an inconspicuous condition, 

 in all cane fields. 



It is usually assumed, and the evidence as a whole supports 

 the idea, that while the root fungi normally exist on dead or 

 senescent material they are able to attack and injure the plant 

 when its vigour is for any reason depressed. The amount of 

 this injury cannot be exactly determined, for it must in the 

 nature of the case be exceedingly variable. The adverse condi- 

 tions which enable such injury to take place produce their own 

 direct effects, and it is in all cases a matter of judgment to what 

 extent the action of the fungus has increased them. 



In accordance with these characters root disease may be 

 regarded in either of two ways : 



(a) as a condition of ill-health non-parasitic in its origin, 

 increased to a varying extent by secondary infestation with semi- 

 parasitic fungi ; or 



(6) as a fungus disease for the development of which a 

 weakened condition of the plant is necessary as a predisposing 

 cause. 



The difference is mainly one of phrases, and one or the other 

 conception may be the more appropriate in a given case. 



Distribution. 



The association of the fungus Marasmius Sacchari with a root 

 disease of sugar-cane in Java was described by J. H. Wakker in 

 1895. Root disease in which this fungus among others commonly 

 appears is generally distributed through the West Indian region 

 from Louisiana to British Guiana. It occurs in the Hawaiian 

 Islands and in Queensland and has recently been reported from 

 South Africa. 



In the West Indies the fungus was first recognised and its 

 relation to root disease described by A. Howard. The affection 

 has been discussed by every mycologist who has had to do with 

 sugar-cane in these regions, but almost entirely in general terms. 

 There is need for detailed investigation of the several fungi 

 concerned and their relationship to the plant, but from the 

 nature of the case this study to be complete would need to include 

 the whole ecology of the sugar-cane. 



The Associated Fungi. 



Marasmius spp. The fungus most usually associated with 



