SECTION Vir. — ROOT DISEASE OF SUGAR-CANE. 95 



■causes the "root-rot" of tobacco in certain parts of the United States. 

 After carefully planned experiments in which they were able to vary the 

 conditions one at a time they found that the most important factor was 

 the temperature of the soil, and that at 20° C. (68° F.) the fungus is an 

 active parasite and rapidly destroys the roots of the tobacco plant while 

 at 30° C. (86° F.) it has little or no influence and the plant grows 

 vigorously. ■ A series of experiments of this nature could not fail to 

 throw important light on the problems in connection with the root 

 disease of sugar cane. 



ROOT DISEASE IN TRINIDAD. 



In Trinidad the two types of roob fungus are to be found throughout 

 the sugar districts, one or other, and occasionally both, being present in 

 almost every field in small quantities. On the whole the Odontia type 

 is more abundant than the Marasmias. The former can be found in 

 the fruiting stage at almost any time in the wet season, but the 

 fructifications of the latter are not common. They have however been 

 found as early as the 10th June, and as late as the 30th December, and 

 probably occur at all times in the wet season under suitable local 

 conditions, which appear to be provided by a saturated atmosphere after 

 ■comparatively dry weather. 



There are at least two species of Marasmius on sugar-cane in Trinidad 

 in one of which the stalk of the mushroom is white and in the other 

 purple- black. 



Root fungi have been seen attacking plant-canes just sprouting and 

 ■occasionally damage well-grown plant-canes, but it is on ratoon canes 

 ■that they are most abundant and that the injury is most severe. 



The difference between uncomplicated root fungus attack and the 

 Trinidad blight, and the possible association between the two are 

 -discussed in Section IX. 



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