D. R. HOAGLAND 



pathological symptoms resulting from a marked deficiency in the 

 medium of some one of the essential inorganic elements. Valuable as 

 this information is for the purpose in view, it does not advance our 

 understanding of the biochemistry of plants in a manner at all com- 

 parable with the advances made in the study of animal tissues or of some 

 microorganisms, in which definite steps in a series of chemical reactions 

 are identified or reasonably deduced from experimental data. 



The use of the artificial culture methods of plant nutrition makes 

 feasible the growing of plants of many species with any desired combi- 

 nation of inorganic nutrients, or with a given nutrient available in 

 graduated quantities. Controlled modifications in the inorganic 

 composition of the plant are thereby induced, although generally in 

 no simple relation to the composition of the nutrient solution. As 

 already stated, possibilities exist for control of illumination and tem- 

 perature and, thus, to some degree for control of carbon assimilation 

 and rates of metabolic reactions. 



It is tempting to propose that these methods of controlled culture 

 afford techniques for endless rewarding studies on biochemical mecha- 

 nisms in the plant. To what extent this is a realistic view is 

 difficult to say. The extraordinary complexity of the growing plant 

 and of the conditions of its nutrition may set narrow limits to what 

 can be done of fundamental biochemical importance, but whatever 

 opportunities do exist have yet to be adequately explored. There are, 

 of course, other methods of experimentation on plants which can be 

 adapted to biochemical research, such as embryo culture, culture of 

 root tips, and experiments with excised leaves, roots, or other parts of 

 the plant immersed in solutions of known composition. A technique 

 has been recently described (13) for physiological and chemical studies 

 on albino plants, whereby the transformations of a known carbo- 

 hydrate supplied to the plant might be followed, without being com- 

 plicated or obscured by reactions which are associated with photo- 

 synthesis. 



It may be noted again that from the standpoint of plant nutri- 

 tion the main biochemical problem is the fate of the chemical elements 

 derived from the nutrient medium and the way in which they interact 

 with the products of photosynthesis. Most of the elements essential 

 to plants are also essential to all organisms; research on their metabolic 

 functions has therefore a wide biochemical interest. For some cf 



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