262 



A NEW ROOT ROT DISEASE OF COTTON. 



In response to a circular letter issued from the Alabama Agricultural 

 Experiment Station during the early part of the summer of 1890, re- 

 questing specimens of cotton affected with the so-called " black rust,'^ 

 " red rust," " root rot," etc., I received specimens of rotted roots of cot- 

 ton from Saville, Alabama. The specimeus were sent by Mr. G. W. 

 Ehodes, of that place, on whose farm they were collected. The disease 

 was called by him '' root rot," and the roots were certainly in quite an 

 advanced stage of decay. The two roots sent were tai)roots and were 

 probably pulled up so that the decayed lateral roots were broken away. 



I expected to find the Ozonium described by L. H. Pammel as being 

 the cause of a root-rot disease of cotton in Texas. (Bulletins Nos. 4 

 and 7, Texas Agricultural Experiment Station.) There were no ex- 

 ternal signs of the mycelium of a fungus visible to the unaided eye, 

 and my examination was made by taking cross-sections. 



In all the preparations fungus threads were present, having penetra- 

 ted the dead tissue. I supposed these were probably connected with 

 the Ozofiiuniy though we would expect to find various saprophytic fungi 

 attacking such tissues. In one preparation, however, peculiar fat glob- 

 ules were present in quantity in enlarged cavities. Upon close exami- 

 nation I found also pieces of a thin membrane marked with irregular 

 rugosities and striae. 



This at once suggested tome the presence of the female cjsts of Reter- 

 odera radicicola, a root-gall I:^ematode, which was made the subject of 

 a special study by myself one year ago, and is known to be very inju- 

 rious to many plants. 



The subject now possessed a new interest and I made a special trip 

 to Saville the early part of September to thoroughly investigate the 

 disease and to make careful collections of plants in various stages. 

 Although I possessed the faint suggestions of the presence of Hetero- 

 dera in the material sent me I was quite surprised to find that this 

 worm was the cause of the disease. 



There were perhaps 2 or 3 acres in the field that were more or less 

 affected. In some places there were spots several square rods in extent 

 on which the cotton was entirely dead. These spots were often con- 

 nected by areas more or less affected, and in some places an apparently 

 healthy plant was surrounded by dead ones. The plants I examined 

 were carefully dug up with a shovel. At first I selected those entirely 

 dead. Only a portion of the taproot remained attached to the stem, 

 the lower portion having rotted away. To the plants which had re- 

 cently died portions of the lateral roots remained in connection, the 

 majority, however, easily breaking away. 



In a few cases, even though the roots were well rotted, the charac- 

 teristic galls could be seen on some of the lateral roots, being oval and 

 somewhat one-sided enlargements. On the decayed taproots no galls 



