DISEASES OF SUGAR CANE 293 



difficult to estimate. Senescence and death of the older roots is to 

 some extent normal, and changes in aeration brought about by 

 the saturation or packing of the soil frequently cause the gradual 

 replacement of the deeper roots by others nearer the surface, 

 without necessarily producing much effect on growth so long as 

 the weather is favourable. The most that one can usually say in 

 moderate cases is that the number of functioning roots is less 

 than one would expect to find in the situation, or than is found in 

 normal plants at the same stage. It is also possible to trace a 

 certain amount of invasion of the young roots by the hyphae of 

 the fungus ; th 'r tips are frequently brown and dead, the cortex 



Fig. 117 



HiMANTIA STELLIFERA, HyPHA WITH STELLATE CRYSTAL AND SWOLLEN 



Bodies 

 From Bull. Porto Rico Ins. Expt. Sta. 



is red or brown in spots, and considerable distortion may be 

 present as a result of interference with the growing tips. 



In the acute type of root disease later described, the ability 

 of Marasmius to become parasitic on roots, buds, shoots and 

 stem bases is convincingly demonstrated, and it is reasonable to 

 assume that, in the general type now under discussion, this 

 ability is exercised to some extent. 



Conditions of Occurrence. 



The condition of infestation described is very rarely 

 general and uniform over a whole field. Typically it 

 occurs in its pronounced form in patches related to the 



