191S.] PUBLIC DOCITINIENT — No. 31. 37a 



practical features of the investigation. It is believed that a 

 satisfactory means of controlling the disease has been worked 

 out. 



For several years a disease of lawn grass, which is evidenced 

 by the dying of the grass in round areas a foot or more in diam- 

 eter, has been under observation. Repeated attempts to de- 

 termine the cause of this trouble had failed to connect any 

 pathogenic organism with it until last summer, when our efforts 

 were rewarded by the isolation of a fungus which we have since 

 proved to be the causal agent of the disease. The fungus proves 

 to be an unnamed species of Sclerotium, and will be named and 

 described in a later publication. Control measures are under 

 investigation. 



Investigations on rust of Antirrhinum, a serious disease of 

 this floral crop both in the greenhouse and out of doors, have 

 established a method of control under glass, and results will be 

 presented for publication at an early date. 



The complete results of the investigations on mosaic disease 

 of tobacco were published in a bulletin issued during the year. 

 On the completion of this work G. H. Chapman was assigned 

 to a new project for the study of so-called "tobacco-sick soils," 

 referred to in our last annual report.^ This project has been 

 established on an experimental basis. Three plots for study of 

 fertilizer and soil reactions, and one for chemical treatment of 

 soil infected with the root-rot fungus {Thielaxia hasicola (B. & 

 Br.) Zoff), were conducted during last summer. Many soil 

 samples have been taken for laboratory tests and much data 

 gathered on various factors. Physiological studies of Thielavia 

 are being made with a view to establishing a soil reaction favor- 

 able to the development of tobacco and unfavorable to the 

 fungus. This work has awakened keen interest on the part of 

 tobacco growers, who are more than ever looking to the station 

 for help in solving some of their important problems. 



The project for the study of the response of plants to light, 

 in charge of O. L. Clark, was extended to include field work 

 last summer. A number of crops were grown under cloth of 

 different textures which cut off varying amounts of light, with 

 a suitable check plot in the open. The tents were so designed 



> Twenty-ninth annual report, Mass. Agr. Expt. Sta., 1917, p. 63o. 



