WATER-CULTURE METHOD — HOAGLAND AND ARNON 463 



so far to plants developed in soil and has no essential relation to the 

 water-culture method of growing plants. 



HISTORICAL SKETCH OF THE DEVELOPMENT OF THE WATER- 

 CULTURE METHOD 



Curiously enough, the earliest recorded experiment with water 

 cultures was carried out in search of a spurious "principle of vegeta- 

 tion" in a day when the general ignorance of the principles of plant 

 nutrition seemingly precluded the undertaking of a profitable experi- 

 ment. Woodward, about 1699, grew spearmint in several kinds of 

 water: rain, river, and conduit water to which he in one case added 

 garden mold. He found that the greatest increase in the weight of 

 the plant took place in the water containing the greatest admixture 

 of soil. His conclusion was, "That earth, and not water, is the matter 

 that constitutes vegetables." 



The real development of the technique of water culture took place 

 about three-quarters of a century ago and came as a logical result of 

 the crystallization of the modern concepts of plant nutrition. By 

 the middle of the nineteenth century, enough of the fundamental 

 facts of plant physiology had been accumulated and properly evaluated 

 to enable the botanists and chemists of that period to assign correctly 

 to the soil the role which it plays in the nutrition of plants. They 

 realized that plants are made of chemical elements obtained from three 

 sources: air, water, and soil; and that the plants grow and increase 

 in size and weight by combining these elements into various plant 

 substances. 



The major portion, usually about 90 percent, of the dry matter 

 of most plants (water is, of course, always the main component of 

 growing plants) is made up of three chemical elements: carbon, oxygen, 

 and hydrogen. Carbon comes from the air, oxygen from the air and 

 from water, and hydrogen from water. In addition to the three 

 elements named above, plants contain other elements, such as nitrogen, 

 phosphorus, potassium, and calcium, which they obtain from the 

 soil. The soil, then, supplies to the plant a large number of chemical 

 elements, but they constitute only a very small portion of the plant's 

 composition. It was early understood, however, that various elements 

 which occur in plants in comparatively small amounts are just as 

 essential to their growth as those which compose the bulk of plant 

 tissues. 



The publication, in 1840, of Liebig's book, The Application of 

 Organic Chemistry to Agriculture and Physiology 2 in which the 

 above views were ably and effectively brought to the attention of 

 plant physiologists and chemists of that period, served as a great 

 stimulus for the undertaking of experimental work in plant nutrition. 



1 Von Liebig, Justus, Chemistry in its applications to agriculture and physiology, English trans., 401 pp . 

 John Wiley, New York, 1861. 



