WATER-CULTURE METHOD — HOAGLAND AND ARNON 467 



quately aerated, and with light excluded; a porous bed may be con- 

 venient as a means of facilitating aeration of the solution, as a heat 

 insulator, or as a support for the plant, but plays no indispensable 

 role. Aside from such considerations, the choice of a covering is 

 determined largely by expense and convenience, provided the materials 

 used are not toxic to plants. 



With any kind of covering for the tanks, an adequate supply of air 

 to the roots must be provided. While the use of a porous bed instead 

 of a perforated cover facilitates aeration of roots, the bed can be dis- 

 pensed with if provision is made to bubble air through the nutrient 

 solutions (pi. 1). Kecent experiments have shown that even with the 

 use of a porous bed, bubbling air through the solution may be advan- 

 tageous or, under some conditions, indispensable. 



For approximately a quarter of a century investigations have been 

 conducted at the University of California on problems of plant nutri- 

 tion with the use of the water-culture technique, as one important 

 method of experimentation. The objective has been to gain a better 

 understanding of fundamental factors which govern plant growth, in 

 order to deal more effectively with the many complex problems of soil 

 and plant interrelations in the field. As illustrations of some scientific 

 problems of plant nutrition which have been elucidated by the aid of 

 the water-culture method of experimentation, the effects of aeration 

 of the roots on plant growth are shown in plate 2, figure 1, and the 

 effects of deficiencies of mineral elements required in minute quantity 

 in plate 2, figure 2. 



Many workers have participated in these investigations. One of 

 them, W. F. Gericke, conceived some time ago that the water-culture 

 method, hitherto employed only for scientific studies, might be 

 adapted to commercial use. In experiments carried on in the green- 

 houses and experimental gardens of the university, he grew plants in 

 water culture on a scale larger than that used in earlier investigations 

 and devised a method of superimposing a porous bed over the nutrient 

 solution. This development was soon given widespread publicity in 

 newspapers and popular journals. The public became fascinated 

 with the idea of growing plants in a medium other than soil. Many 

 thousands of inquiries have come to the University of California 

 requesting detailed information which would make possible the general 

 application of the water-culture method by commercial concerns or by 

 amateur gardeners. 



This article, based largely on experience of its authors, was pre- 

 pared to make available information for which a great public demand 

 had arisen. Although in view of the complexity of the problem the 



• The authors, however, disclaim any credit for suggesting the use of the water-culture method for com- 

 mercial purposes. 



114728—39 31 



