DISEASES OF PLANTS. 155 



yield is very materially dimiuished. Diseased tubers show discoloration when 

 cut across, and all such should be rejected in planting. The disease is not 

 a new one, but it has only lately become prominent. 



A leaf spot disease of sisal in German East Africa, K. Braun (Bcr. Land u. 

 Forsiic. Dciitsch-Ostafriku, J (UJOS), No. ',, pp. 1-',S-166, pi. i).— In 1905 a 

 peculiar spotting of sisal leaves was reported, and in 1906 the author visited a 

 number of plantations and found the spotting more or less common in all 

 localities. 



The trouble seems to be due to high temperature and weather conditions, no 

 plant or animal parasite being found to be associated with it. It appears 

 that under certain conditions the sun burns the tissues of the leaves, and that 

 later sunken, discolored areas appear, due to the destruction of the underlying 

 tissues. All leaves do not seem to be equally subject to the spotting, those 

 standing most nearly vertical being less injured than the spreading ones. The 

 author was able by artificial means to produce the spotting without any action 

 of the sun. As would be expected from the nature of the cause, the underside of 

 the leaves is less subject to injury than the upper. 



The smuts of sorghum, E, M. Freeman and H. J. C. Umberger ( U. S. Dept. 

 Agr., Bur. Plant Indus. Circ. 8, pp. 9). — A description is given of the sorghum 

 smuts, 2 forms of which are recognized, the grain, or kernel, smut {Sphace- 

 lotltcca sorghi) and the head smut iS. reiliana). 



The grain, or kernel,* smut is easily distinguished by the fact that only the 

 individual kernels, or grains, are affected, while the head retains its usual 

 form and nearly its usual appearance. 



The head smut is quite different in appearance. The whole head just as it 

 emerges from the upper leaf is converted into a single large smut mass, covered 

 by a whitish or grayish membrane, which soon bursts and sets the spores free. 

 In this smut all trace of the individual grain is lost, and the smut mass 

 resembles somewhat that of a smut mass on corn. 



Of the 2 forms of smut, only the kernel smut is at present widely distributed, 

 and experiments have shown that this can be readily controlled by treating the 

 seed either with formaldehyde or hot water. Copper sulphate has also given 

 satisfactory results, but is not to be preferred to either of the other treatments. 



The head smut at present is known to occur in abundance only in a restricted 

 area in the Panhandle region of Texas, and the only recommendation that can 

 i)e made at the present time is to keep it away from the farm and the com- 

 munity. In order to do this, care must be exercised to obtain seed from regions 

 where the head smut does not exist. 



So far as now known, milo maize has not been reported as subject to either 

 disease, and it may probably be safely grown without treatment. 



The field treatment of tobacco root rot, L. J. Briggs (U. 8, Dept. Agr., Bur. 

 Plant Indus. Circ. 7, pp. 8 ) . — During the past few years a root rot of tobacco, 

 due to Thiclavia basicola, has been reported from the tobacco districts of 

 Kentucky, Connecticut, Ohio, and Wisconsin (E. S. R., 16, p. S86; 18, p. 1139). 

 The root rot has been successfully checked in the seed bed by the use of for- 

 malin and through steam sterilization, but neither of these means is practicable 

 for its control under field conditions. The author carried on some prelimi- 

 nary experiments with fertilizers which seemed to indicate that tobacco is 

 nuich more severely injured by the fungus in the fields where the soil has 

 l)een made alkaline by the long-continued use of large amounts of lime, ashes, 

 and fertilizers containing carbonate of potash. 



P.y field and greenhouse exi)eriments it was found that the alkaline condi- 

 tion of the soil favored the development of the root rot, and as a remedy it 



57401— No. 2—08 5 



