130 VEGETABLE FORCING 



In this connection it is stated, in the Market Growers' 

 Journal, that by merely watering bed surfaces with a hose, 

 little moisture reaches the foliage, and thus the bordeaux 

 mixture does not become effective. To the writer the 

 explanation lies in the* need of atmospheric moisture to 

 make the copper compounds soluble in bordeaux mixture. 

 Wherever, therefore, there is in greenhouse practice no 

 moistening of the foliage, bordeaux mixture will not 

 become available for fungicidal effect to any considerable 

 extent. 



It is important, therefore, to maintain a supply of soil 

 moisture sufficient to cause normal growth. It also seems 

 that inadequate soil moisture, which may cause a slow, 

 weak growth, makes the plant more susceptible to cer- 

 tain diseases. 



The influence of temperature. Very high temperature 

 in the greenhouse may render the plants susceptible to 

 disease. No harm will result from high temperature if 

 there is sunshine, normal soil moisture conditions and 

 proper ventilation. But excessive heat and high humidity 

 in the absence of sunshine are certain to cause very rapid 

 growth and soft, tender tissues which are most sensitive 

 to diseases. High temperatures and abundant moisture 

 also provide the most favorable conditions for the germi- 

 nation of spores and the further progress of diseases. 

 Great extremes in temperature should be avoided because 

 they are not conducive to the strongest growth of the 

 plant. 



Vigor of growth. It is universally conceded that 

 greenhouse plants which are making a normal, vigorous 

 growth are the least susceptible to disease. It behooves 

 the grower, then, to maintain soil and atmospheric condi- 

 tions which are most favorable to the plants under culti- 

 vation. This involves careful and intelligent fertilizing, 

 watering and ventilating. There must be no neglect in 

 firing the boilers or in any other operation that is essential 

 to the growth of disease-resistant plants. 



