480 ANNUAL, REPORT SMITHSONIAN INSTITUTION, 19 3 8 



DIRECTIONS FOR GROWING PLANTS BY THE WATER-CULTURE 



METHOD 



TANKS AND OTHER CONTAINERS FOR NUTRIENT SOLUTIONS 



Various kinds of tanks have been utilized for growing plants in 

 water culture. Tanks of black iron, well painted with asphalt paint 

 (most ordinary paints cannot be used because of toxic substances), 

 have proved satisfactory for experimental work. Galvanized iron 

 may give trouble, even when coated with asphalt paint, if the paint 

 scales off. 



Concrete tanks have been tried, but they may require thorough 

 leaching before use. Painting the inside of the tank with asphalt 

 paint is advisable. Wooden tanks will serve the purpose, if made 

 watertight. Redwood may give off toxic substances and therefore 

 may require preliminary leaching to remove these substances. Final- 

 ly, coating with asphalt paint is desirable. 



For small-scale cultures, 2- or 4-gallon earthenware crocks may 

 be serviceable. A wire screen to hold the bedding material can be 

 bent over the sides of the crock. But if a number of plants are to 

 be grown to large size in such jars, the solution may require special 

 aeration as by bubbling air through it continuously. 



For demonstrations in schools, Mason jars covered with brown 

 paper, to exclude light, can be employed (pi. 5). The jars are pro- 

 vided with cork stoppers in which one or more holes have been bored 

 (sometimes a slit is also made in the cork; see fig. 1). Plants are 

 fixed in the holes with cotton. Wheat or barley plants are very suit- 

 able for these demonstrations, since they may be grown in the jars 

 without any special arrangements for aeration. 



Other types of culture vessels are shown in plate 6. 



The dimensions of tanks must be selected in accordance with the 

 objective. One kind of tank, of moderate size, adapted to many 

 purposes, has dimensions of 30 inches in length, 30 inches in width, 

 and 8 inches in depth (pi. 6, B). A smaller tank, 30 inches long, 

 12 inches wide, and 8 inches deep, is convenient for use in many 

 experiments (pi. 6, C). In general, shallow tanks will be found 

 suitable. The length and width may be determined by consideration 

 of convenience and economy. As an alternative to the porous bed, 

 for many kinds of plants, tanks can be provided with metal or wooden 

 covers perforated to hold corks in which plants are fixed with cotton, 

 if adequate aeration is maintained (pi. 2). 13 (See discussion of aera- 

 tion, p. 467.) 



" A description of the construction of aerating devices for culture solutions is given by: Furnstal, A. F., 

 and Johnson, S. B., Preparation of sintered pyrex glass aerators for use in water-culture experiments with 

 plants. Plant Physiol., vol. 11, pp. 189-94, 1936. 



