siderable root disease has been found, the lack of evidence of the 

 presence of Marasmins sacchari in any amount, transfers the discus- 

 sion to the account of the mottling disease itself. 



Injury. — The injury caused is primarily upon the roots. The 

 mycelium enters the roots, distintegrates the tissues and prevents a 

 proper absorption of water and nutriment from the soil. As a result 

 of this injury to the roots there is the secondary effect upon the 

 development of the plant. According as the attack is sever or mild, 

 the host shows a varying amount of leaf curling, a dwarfing of the 

 stool, and often an early succumbing to less vigorous parasites such 

 as Melanconium. 



Injury to the roots can be ascertained by direct examination, a 

 slow tedious process, or to a certain extent can be diagnosed by 

 symptoms above ground. The fungus itself eventually appears on 

 the cane above ground, growing within and upon the lower leaf- 

 sheaths, some times one-half or two-thirds the height of the stalk. 

 The external appearance is a white mycelial growth, which is con- 

 spicuous by its rather smooth membranous appearance in contrast 

 to a distinctly filamentous growth. Tearing away the affecteci leaf- 

 sheaths reveals the fact that they are decayed, and are glued together 

 as it were by the membranous growth, to the underlying sheaths and 

 the stalk. The decay of the lower leaf -sheaths may not in itself be 

 of great importance, but the binding of the leaf-sheath to the stem 

 is very undesirable from the point of view of the mill worker who 

 prefers clean cane. 



This fungus, like some others, appears to make great headway 

 when once it has attained a strong foothold on the host. Thus the 

 fungus may develop well on plant cane without doing appreciable 

 injury, but may so increase its foothold on the ratoons as to do double 

 the injury. As a result of this action it is a common sequence that 

 plant crops are fair in certain localities, the first ratoon is consider- 

 ably poorer, and the second ratoon often dies out completely. The 

 damage may be restricted to one or a few stalks in a stool, or more 

 commonly it may affect an entire stool as well as one or more adjacent 

 stools to form the eharacteristic disease spots, or more rarely large 

 portions of fields are entirely affected. 



The injury to the plant may he considered threefold : the growth 

 of the plant is checked often to tlic point wlun-e no merchantable 

 cane is produced, the matter of clean cane is rendered difficult, and 

 file cane becomes more susceptible to other diseases. 



Loss. — To estimate the loss caused by a disease of this nature is 

 alw.-iys a complicated innftcr niid foi- tli;i1 fejison nsiially highly nnsat- 



184 



