DISEASES OF SUGAR CANE 295 



shoots and abundant new roots and continue to thrive so long 

 as the conditions are favourable. In the same way fields of 

 ratoons which have been infested in a dry year and have given 

 next to no return have produced good crops when the following 

 year provided suitable weather. This is in strict conformity with 

 the nature of the disease as set out above, and no such recovery 

 can be expected where the soil is in a defective condition. 



Infection. 



It is not at all uncommon for cuttings and especially for top 

 plants to have root fungus present upon them in a living con- 

 dition when they are put into the ground. It is in fact the 

 custom of some planters, from motives of economy, to take their 

 plants from their worst fields, which in many cases are running out 

 owing to infestation with this disease. Such material may give 

 quite good results in a favourable season, but the fungus is present 

 from the beginning, ready to take advantage of any unfavourable 

 circumstance that may occur. Infection may also take place from 

 the old stools left in the ground, from imperfectly rotted trash 

 and, where there has been no suitable rotation of crops, from 

 mycelium present in the soil. Ratoons are especially liable to 

 infestation owing to the fungus which has gained a footing on the 

 plant canes attaining to a vigorous development on the material 

 thrown out of action when the first crop is cut, at the same time 

 that the effect on the plant of the progressive deterioration of 

 the unworked soil affords it increasing opportunities for harm- 

 fulness. The spores of the fungus afford another means for 

 its dissemination, but of this nothing is directly known. 



Varietal Resistance. 



In a given locality there are stronelv marked differences in 

 the susceptibility of sugar-cane varieties to root disease. It is 

 questionable, however, how far resistance or susceptibiUtv can be 

 regarded as constant varietal characters. It is the writer's 

 opinion that canes which are well or ill-suited to a particular 

 district, especially in regard to soil, show differences in vigour 

 which are reflected in their relative liability to root disease. A 

 cane which has an excellent reputation in one place may have a 

 very poor one in another, and various degrees of such differences 

 give rise to the strong and varied local preferences which 

 exist. 



Under present conditions the Bourbon and B 208 appear to 

 be the most widely susceptible of standard kinds ; both require 

 soils in good tilth to succeed. To these C. K. Bancroft added 

 D 625 and Green Transparent from British Guiana experience, 

 with D 109 rather susceptible, D 145 and D 118 more resistant, 

 and D 216 and D 159 not affected. White Transparent shows an 

 increase of susceptibility over most other varieties in the dry 



