1910.] PUBLIC DOCUMENT — No. 31. 159 



We have recently seen another case in which the phmts in 

 a range of houses about 1,800 feet in length were more or less 

 affected. Besides the application of horse manure for a num- 

 ber of years, the houses had been treated with cow manure, va- 

 rious kinds of phosphates, nitrate of soda, lime, hen manure 

 and pulverized sheep manure, as well as hot water. Different 

 types of greenhouses were represented in this establishment, and 

 the houses were also of different ages. The older houses, which 

 had been manured and fertilized the most heavily, were decidedly 

 the worst. The new houses, where less manure and fertilizer 

 had been applied, were least affected. In the older houses it 

 had become almost impossible to grow good crops of cucumbers, 

 but fairly goods crops were growing in the new houses. These 

 houses had been used occasionally for growing other crops, 

 like tomatoes and radishes, which were not affected in any way. 

 This practice of rotation is beneficial, and has a tendency to 

 make the soil more suitable for cucumber growing. 



The extensive use of nitrate of soda is responsible for many 

 cases of malnutrition. We have demonstrated by experiments 

 that potted plants of cucumbers watered with potassium or 

 sodium nitrate will wilt in the sunshine more quickly than those 

 treated with water alone. Nitrate of soda, when used in green- 

 houses, often acts by preventing root absorption. As a conse- 

 quence of this reduction of the root absorptive capacity of the 

 plant, particularly when the house is warm and dry and trans- 

 piration very active, the leaf edges of the cucumber wilt and die, 

 which causes a rolling of the leaf or convexity of the upper 

 surface. 



Wetting down the soil with hot water, or steaming it, as al- 

 ready pointed out, is favorable to malnutrition, for the reason 

 that a considerable amount of plant food already in the soil is 

 by this practice made more available. This is shown by the 

 greatly increased growth of plants in such soil, and the in- 

 creased number of bacteria present. 



In the growing of greenhouse crops of all kinds, manure is ex- 

 tensively used. For example, lettuce has been grown for forty 

 years in soil which has been repeatedly manured with horse 

 manure and straw, and no indications of malnutrition caused 

 by this extensive manuring have ever been noticed. It is gen- 



