20 a EXPERIMENT STATION. [Jan. 



Optimum Conditions of Light for Plant Response. — Prof. O. 

 L. Clark has continued to accumulate experimental data in his 

 study of optimum light requirements of plants. That phase of 

 the work embracing study of the influence of different light in- 

 tensities on plants grown under cloth of different meshes has 

 been discontinued after several years of field tests. A new 

 feature of this work now being planned will ^leal with the 

 influence of ultra-violet light on plants. 



Plant Diseases of the Year. 



While the plant diseases coming under our observation were 

 as numerous and varied as in almost any other year, few new 

 or unusual troubles were among them. 



Tohacco. — A bacterial disease of tobacco, known in the 

 South as wildfire, was reported for the first time in this State, 

 though there is evidence to support the belief that it was 

 present at least two years earlier. During the ciu^ing and 

 fermentation season for tobacco, the weather conditions favored 

 development of such troubles as pole-sweat, stem-rot, canker 

 and moldy or musty tobacco. Considerable loss ensued, and 

 there were many calls for assistance. An Extension bulletin, 

 entitled "Curing and Fermentation Troubles of Tobacco," and 

 an Extension circular on "Tobacco Wildfire," were prepared by 

 Dr. Chapman. 



Tomato. — Late in September, Septoria leaf-spot of tomato, 

 caused by Septoria lycopersici Speg., was discovered in a small 

 garden in Amherst where it had caused severe defoliation of the 

 vines. The disease previously has been noted on two occasions 

 in greenhouses of the State, but this is the first report of its 

 occurrence out of doors in Massachusetts. In the ^Middle 

 Atlantic States this disease causes large losses, and is rated as 

 the most serious disease of the tomato in that region. Should 

 it gain a foothqld in this State it might become a problem of 

 considerable economic importance. 



Carrot. — What appears to be a new disease of the carrot was 

 first called to our attention in 1918 at the Market-Garden Field 

 Station by Prof. 11. F. Tompson. The disease seems to be 

 very destructive at times, and while it received some attention 

 in 1919 and 1920, it is deserving of careful investigation, and 



