478 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 8 



nutrient solutions, each one best for a given species of plant. Some 

 general type of solution such as those described in this circular, 

 should be tried first and modified later if necessary as a result of 

 experimentation. 11 



INSECT ATTACKS AND DISEASES 



Contrary to some statements, it is not true that plants grown by 

 the water-culture method are thereby protected against disease 

 (except strictly soil- borne diseases) or the attacks of insects. Recent 

 observations suggest that diseases peculiar to the water-culture method 

 may sometimes attack plants grown in nutrient solutions. 



WATER REQUIREMENTS OF PLANTS GROWN BY THE WATER- 

 CULTURE METHOD 



The use of water by plants is primarily detennined by the physio- 

 logical characteristics of each species of plant, extent of leaf surface, 

 and atmospheric conditions, just as when plants are grown in soil. 

 If a large crop is produced, either by the water-culture method or in 

 soil, and if climatic conditions favor high evaporation of water from 

 the plant, the amount of water used in producing the crop is neces- 

 sarily large. 



In a greenhouse experiment conducted in Berkeley for the purpose 

 of comparing the growth of tomatoes in soil and water-culture media, 

 according to actual measurement, somewhat more water was required 

 to produce a unit weight of fruit under water-culture conditions than 

 under soil conditions. Possibly more water was evaporated from the 

 water surface than from the soil surface, in addition to the principal 

 loss of water by evaporation through the plant, common to both 

 soil and water culture. The fallacy of the idea that plants could be 

 grown in a desert region with a fraction of the water needed to pro- 

 duce crops in irrigated soil is evident, assuming any reasonably good 

 management of irrigation practices. 



RESUME OF THE WATER-CULTURE TECHNIQUE 



Many types of containers for nutrient solutions have been found 

 useful. In investigational work, 1- or 2-quart Mason jars provided 

 with cork stoppers often serve as culture vessels (pi. 5). Sometimes 

 5- or 10-gallon earthenware jars have been found suitable for experi- 

 mental purposes. Small tanks of various dimensions have been 

 extensively used. For certain special investigations, shallow trays 

 or vessels of Pyrex glass are required. The selection of a container 



11 A number of inquiries have been received regarding the culture of mushrooms. The water-culture 

 method under discussion is unsuited to the culture of mushrooms. These plants require organic matter 

 for their nutrition, and differ in this way from green plants, which can grow in purely mineral nutrient 

 solutions like those described in this circular 



