64 MASSACHUSETTS HORTICULTURAL SOCIETY. 



In view of what has been said, it is perhaps not surprising that we 

 should find in horticultural and plant disease literature, after unusual 

 seasons, notes on new or previously little known disease-producing 

 organisms. Some of these organisms remain in the role of disease 

 producers, while others may never again be mentioned, or at most 

 only at intervals. In many cases it is justifiable to assume that 

 unusual conditions of the en^dronment are operative on the host 

 plants, the fungi, or both, — so affecting the balance between the 

 host plant and the disease organism that tissues formerly resistant 

 are penetrated, or that a fungus ordinarily weak is rendered more 

 virulent. 



It seems to be well established that there may be such a thing as 

 progressive virulence during successive generations of a fungus, 

 just as there may be progressive losses of virulence. It has been 

 shown in the case of certain bacterial diseases of animals that a 

 certain variation in \irulence resides in the bacteria, but the condi- 

 tion of the animal organism is likewise important and a general 

 delicacy of constitution, unusual exposure, or in certain cases any 

 condition producing a low obsonic relation is of importance in 

 determining effective infection, or the intensity of reaction to the 

 attack. 



Discussion. 



The question was asked if there were any new methods to be 

 recommended in the treatment of fungous diseases of pears. 



The Lecturer in reply said that no new methods had been de- 

 veloped but the necessity of early and effective spraying should be 

 emphasized. Early spraying prevents the disease getting a start 

 from spores which have been harbored by bark, bud scales, etc. 



George D. Moore inquired concerning a remedy for mildew of 

 lettuce grown under glass. 



The Lecturer stated that it was very difficult to prevent the start 

 of mildew. It may be kept under control to some extent by thor- 

 ough ventilation and surface drainage. The soil of the house also 

 should be frequently changed. 



An inquiry was made for a simple method of testing soil to de- 

 termine its acidity or alkalinity. 



