[Vol. 2 



424 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



growth on cotton decoction starch paste in 1902. Since in 

 general pathology and physiology the cotton Ozonium and the 

 violet Rhizoctonia have much in common, a further careful 

 investigation of their life relations would doubtless yield 

 interesting results. 



PREVENTION' AND CONTROL 



Relief measures respecting the violet fungus are very 

 largely limited to the practices of good culture, good drain- 

 age, and sanitation. The early pathologists have generally 

 recommended pulling up diseased plants and burning them. 

 It is well to point out, however, that after a careful examina- 

 tion of the distribution of the fungus on the smallest fibrous 

 roots, it has been found to invest these to a considerable 

 depth in the case of alfalfa, and therefore a very small meas- 

 ure of security may be expected unless one carries out this 

 recommendation in a far more thorough manner than is 

 practicable in the field. The further suggestion has been 

 made that where the diseased areas are few, small, and clearly 

 defined, trenches may be dug to prevent the further spread of 

 the disease; but if this should prove feasible under any con- 

 ditions, it would be advisable only in connection with a thor- 

 ough disinfection of the isolated areas by formaldehyde or 

 sulphuric acid — the former disappearing from soil in time, 

 and the latter being easily neutralized by liming. The rota- 

 tion of crops is undoubtedly desirable, but complete immun- 

 ity from the disease cannot be expected if we may trust the 

 statements of Du Hamel and other observers to the effect 

 that the fungus may remain alive in the soil for periods of 

 from three to twenty years. The fact that many hosts are 

 affected also complicates the practice of rotation. 



The Common Rhizoctonia, R. Solani Kuhn (Corticium 



vagum B. & C.) 



EARLY STAGES 



In addition to his discussion of the violet Rhizoctonia on 

 beets and carrots Kuhn ('58) described a disease of potatoes, 

 of which the causal organism was recognized as a species of 



