308 MASS. KXPKRIMKNT STATION RUI^I.ETIN 21.7 



have given rise to the luuiie brown root-rot. Tlie.se results lend support to 

 the iiypothesis that brown root-rot of tobacco is the expression of the in- 

 jurious etfect on tobacco roots of one or more toxic substances which are 

 formed from, and at certain stages in, the decomposition of vegetable or- 

 ganic matter, more especially the residues of certain slowly decomposing 

 crops sucii as timothy. 



(JheMiical analyses of timotiiy infusions prepared at one week inter- 

 vals were made by Professor Henri D. Haskins. The oldest infusions 

 v/hich in previous experiments were less toxic to tobacco contained the 

 least ammoniacal nitrogen; but the age at which the content of ammoniacal 

 nitrogen was greatest did not exactly coincide with the age at which in- 

 fusions similarly made were in previous exjieriments most toxic to to- 

 bacco. 



Treatment of brown root-rot soil with^formaldehyde is known to result 

 in less of the disease on tobacco subsequently grown on sucii soil. In ex- 

 periments to test the effect of certain acids on brown root-rot, acetic acid 

 was found to have a like effect. 



Neither sulfuric nor nitric acid, in amounts sufficient to lower the pH 

 value of tiie soil 0.2 to 0.3, liad any effect on the brown root-rot of tobac- 

 co grown in this soil. 



In field experiments on land previously planted to timothy which had 

 been jtreceded by corn, the yield per acre of cured tobacco leaf was 16 

 per cent greater in tlie acetic acid-treated plot tiian in tlie untreated 

 check. Orthophosphoric acid gave 17 per cent increase. 



In pot experiments, thorough washing or leaching of the soil was fol- 

 lowed by some reduction in brown root-rot. But water used in leaching 

 did not induce the disease when used to water tobacco grown in steamed 

 soil. 



In the Tillson Farm plots, brovvn root-rot was severe following alfalfa, 

 timothy and alsike clover in the rotation and the intensity of the disease 

 was approximately the same on limed and unlimed plots. 

 Control of Diseases of Greenhouse Vegetables. (E. F. Guba, Waltham). 



Cladosporium Leaf-Mold of Tomatoes. Fundamental studies in the 

 laboratory have included the action of fungicides on germinating spores, 

 the relation of environment to the epidemiology of the disease and the ap- 

 plication of some of the findings to control practices in the greenhouse. 



Of the fungicides tested, only vaporized sulfur proved of merit. Suc- 

 cessful control both in the laboratory and on spring and fall crops in com- 

 mercial greenhouses was obtained by vaporizing sulfur at frequent inter- 

 vals. The utilization of heat in the steam pipes proved impracticable 

 because it is seldom possible to obtain steam pressure sufficiently high 

 to jirovide the proper temperature for active generation of sulfur vapor. 

 Furthermore, few houses are steam-heated in the early fall and in the 

 absence of artificial heat conditions usually prevail which favor epidemics 

 of leaf-mold. It became necessary, therefore, to devise some other method 

 of vaporizing the sulfur. The need was met by the development of simple 

 electrical apparatus for this purpose and the equipment has been in- 

 stalled and succcessfully used in several commercial houses. 



In the study of environmental relations, it was found that spore germ- 

 ination and subsequent vegetative growth of the fungus occur at tempera- 

 tures from 40° to 95°F. with the optimum at 75° to 80°F. Traces of 

 spore germination were obtained at relative humidities of 98 and 99 per 

 cent, but normal and general germination occurred only in a nu")isture- 

 saturated atmosphere and water proved to provide the ideal medium. 



