29 



greater part of our knowledge concerning the control of green- 

 bouse diseases has been derived from the intelligence and skill of 

 the progressive gardeners, whereas, in a case of outdoor crops, the 

 experiment stations have been foremost in offering suggestions for 

 their control. The trained agriculturists _ can consistently give 

 information in regard to the control of specific diseases affecting 

 outdoor crops, with which he is more or less familiar, but in cases 

 of greenhouse crops the methods of treatment are so different, and 

 require such an insight into the plant requirements, that it is almost 

 necessary for one to be an expert grower, or, at any rate, under- 

 stand something about the normal conditions of the crop, before 

 his judgment or advise is worth much. It is necessary, at least, 

 that he should possess a thorough understanding of the influence 

 on plants of the three cardinal factors, heat, light and moisture, 

 and the role they play in the production of normal crops, together 

 with their relationship to the development of disease-producing 

 organisms. Such matters as soil texture and soil fertility also 

 constitute important features which are necessary to understand. 

 The great attention necessary to give to such matters as heat, 

 moisture and light in greenhouse culture is only appreciated by the 

 trained gardener. Some of the most troublesome and disastrous 

 diseases are entirely controlled by the intelligent use of these 

 factors, and others, which are more or less common, could no 

 doubt be controlled or greatly alleviated if modifications in the 

 method of growing certain crops were practicable. 



The benefits which have resulted from spraying out-of-door 

 crops have unfortunately been the means of inducing some to 

 believe that spraying is the only method of treating plant diseases, 

 and where spraying is not recommended as a remedy their enthu- 

 siasm diminishes. We have grown for some years many experi- 

 mental crops in the greenhouse, and we have seldom had occasion 

 to see the need, or possible benefit, to be derived from spraying. 

 In the elimination of diseases from greenhouse crops, the ultimate 

 aim should be to select varieties of plants which are immune to 

 disease, as well as to study and devise conditions which will not 

 favor the development of fungi. The most perfect and the hardi- 

 est plant organism can become diseased in a remarkably short 

 period of time if the conditions that are suitable for its normal 

 requii'ements are changed. For example, the geranium constitutes 

 one of our most hardy greenhouse plants, nevertheless, if such a 

 rugged plant is placed under a bell glass, it becomes sickly in a 

 very short time, and in a few days it will succumb to disease, even 

 when subject to light and supplied with all of the necessary ele- 



