FIFTY YEARS OF PLANT PHYSIOLOGY IN THE U.S.A. 627 



University of Wisconsin, a number of big chemical companies, and practically 

 all agricultural experiment stations. Most of this work is directed toward 

 application of chemical compounds, so that we do not have a good general 

 theory explaining the action of these compounds. A more theoretical approach 

 to the problem of the action of growth regulators is definitely the most im- 

 portant desideratum in this field. 



As already mentioned earlier, photosynthesis has been investigated in a 

 very active fashion, especially during the last quarter century. The approaches 

 followed are the biophysics and biochemistry of CO2 reduction, with little 

 emphasis on the physiology of the process. Spoehr through his work on the 

 photosynthesis of succulents started the work now carried out at the Stanford 

 Laboratory of the Carnegie Institution of Washington by French, Smith, and 

 coworkers. At the Universities of California, Utah, Wisconsin, Minnesota, 

 Illinois, and Chicago, with Calvin, Arnon, Spikes, Stauffer, Brown, Rabino- 

 witsch, Emerson, Franck, and Gaffron and coworkers much work is going on, 

 whereas Van Niel at the Hopkins Marine Station advanced our knowledge 

 about photosynthesis in general by studying this process in bacteria. 



Especially during the last 10 years a most active group of investigators has 

 dedicated itself to the study of plant biochemistry, with Vickery, Goddard, 

 Bonner, Thimann, Hassid, Skoog, Steward, and hundreds of others working 

 on the metabolism of the plant cell, following the pathways of respiration, 

 protein and carbohydrate metabolism, the action of plant hormones, and many 

 other subjects. Being such a young branch of plant physiology, it is hardly 

 surprising that much of the work is still a checking of the extent to which the 

 findings with animal materials can be applied to plants, but in the near future 

 we can expect a real autochthonous Plant Biochemistry to emerge. 



The subject of organ and tissue cultures is a typically American one, and 

 P. White's name will always remain connected with plant-tissue cultures. He 

 first succeeded in the unlimited culture of excised roots in a synthetic medium 

 containing some yeast extract, and later made tissue cultures as well. This 

 work is now carried on in many laboratories, where the yeast extract was 

 found to be replaceable by Vitamins Bi and B,; and niacin for the growth 

 of excised roots and by auxins for callus cultures. 



Problems of radiation, apart from photoperiodism and photosynthesis, have 

 found surprisingly little interest among American plant physiologists, with 

 the Withrows as exceptions. In connection with the use of atomic energy a 

 little work is carried out on plants. But subjects like phototropism are almost 

 in abeyance in spite of the stimulation given to the subject by Galston. 



A subject studied somewhat spasmodically here is the problem of transloca- 

 tion of organic and inorganic substances, and the names of Curtis, Crafts, 

 Bennett, and Biddulph come to mind. 



The problem of plant growth apart from its chemical control has received 

 some attention by investigators such as MacDougal, Reed, and Kraus, and 



