OZOXIUM EOOT EOT O 



roots were worked out, and detailed observations on the condition of 

 the roots of these plants could be made in the laboratory with the aid 

 of the microscope and dissecting tools. The same method was used 

 in excavating plants in a root-rot spot in an alfalfa field, except 

 that a trench was dug from the center out through the outer edge 

 of the circle. With fruit trees, a large hole was dug around the 

 collar of the tree, and the lateral roots were uncovered from this 

 point. Many such root excavations were made at the United States 

 field stations at San Antonio, Tex., and Sacaton, Ariz., in cotton 

 -and alfalfa fields and on fruit trees. 



COTTON 



DETAILED STUDY OF TJXDERGKOUND PARTS 



From one such excavation of cotton roots on July 19, 1924, at 

 Sacaton, Ariz. (pi. 1), the following detailed notes by groups were 

 made: 



Group 1 (four plants) : Tops healthy; under the roots of these plants old 

 cotton roots were found from the previous season with strands of Ozonium 

 hyphse covering their surfaces. While excavating the root systems the 

 hyphse could be traced from this old root to the collar of the plants. A close 

 examination of the roots showed the presence of a few strand hyphse with 

 large-celled hyphse concentrating at certain points. An occasional pseudosclero- 

 tium was also observed. Below the points where the wefts were forming, 

 small depressions in the bark were found. No evidences of any lesions were 

 found on the roots of the plants on either side of this group. It therefore 

 must be assumed that the mycelium overwintered on the old cotton root and 

 that this was the source of infection. 



Group 2 (one plant): Top healthy; no lesions on roots; a few strand 

 hyphse found at collar. 



Group 3 (four plants) : Tops showing signs of wilting; taproots sound 

 below 25 centimeters ; 3 all laterals rotted for 5 to 20 centimeters from point 

 of attachment to taproot, but the ends of all were sound. Strand hyphse. 

 pseudosclerotia, and large-celled hyphse were plentiful at the collar of these 

 plants: bark sloughed off around collar for about 18 centimeters. 



Group 4 (three plants): Plants have been dead for several days; leaves 

 dried and hanging to branches; roots all rotted except at extreme ends of 

 laterals ; very little mycelium present on the dead roots. 



Group 5 (three plants) : Tops just showing first symptoms of wilt; tap- 

 roots rotted for 30 centimeters; laterals rotted for 5 to 10 centimeters from 

 point of attachment ; both taproots and lateral roots sound below for dis- 

 tances mentioned ; presence of mycelial types as described for group 3. 



Group 6 (two plants) : Plants dead for at least two days; taproots rotted 

 for 35 centimeters; laterals rotted except at ends; point of infection at collar, 

 where bark is sloughed off; presence of mycelium as in group 3, but less 

 pronounced. 



Group 7 (four plants) : Plants wilting; taproot rotted for 25 centimeters and 

 laterals for about 15 centimeters; other root portions sound; point of in- 

 fection at collar, where bark can be sloughed off ; mycelial weft heavy around 

 collar of plants. 



Group 8 (two plants) : Tops healthy; all roots healthy except for one small 

 lesion (1 millimeter in diameter) on taproot of one plant; a few strand 

 hyphse observed on collar of plants. 



Group 9 (four plants) : Tops healthy; slight infection found at collar, early 

 stage; only about 10 centimeters of the collar seemed to be involved; lateral 

 roots perfectly sound; one or two lesions extending through bark to stele; 

 mycelium of various types very plentiful. 



Group 10 (two plants): Plants healthy: no mycelium visible with aid of 

 lens on any of the roots. 



8 All measurements were made from the first node on the plants. 



