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diate significance for plant physiology, are in the first place Pregl's contribu- 

 tions to micro-chemistry. These opened the road toward the chemical identifica- 

 tion of biologically active substances which usually are obtainable only in 

 minute quantities. The identification of auxins a and b and of indoleacetic 

 acid as plant-growth hormones by Kogl and Haagen Smit, or the analysis 

 of traumatic acid as a plant-wound hormone by Bonner, English, and Haagen 

 Smit, would have been impossible without such micro-methods. A more thor- 

 ough study would have to take into account the separate contributions of 

 analytical and synthetic chemistry, both so strongly influenced by the de- 

 velopment of micro-chemistry, to plant physiology. 



Of equal importance is the development of chromatography. Its foundation 

 was laid by a plant physiologist, Tswett, who in 1906 separated the leaf pig- 

 ments with an adsorption column. Chemists, such as Zechmeister, perfected 

 this technique and made it applicable to an untold number of analytical 

 chemical problems. It was especially when the adsorption-column chromatog- 

 raphy was complemented with paper chromatography that it became fully 

 effective in biological research. In conjunction with radio-active tracer tech- 

 nique, not only numerous metabolic products, but also metabolic pathways, 

 can be identified. Much of the recent advance in our knowledge of photo- 

 synthesis is due to the application of these techniques, in the first place by 

 Calvin and coworkers. 



Radio-chemistry, based on the new nuclear physics, is the third in the 

 triumvirate of new chemical techniques which are revolutionizing plant 

 physiology. Not only have tracer elements become indispensable for bio- 

 chemistry, but they are of equal importance in studies of translocation of 

 organic and inorganic compounds inside the plant, of salt uptake, of root 

 distribution in the soil, and of many other problems. 



It is utterly impossible for me to be complete in the listing of new develop- 

 ments in chemistry which have contributed significantly to plant physiology. 

 I could mention studies on the nature of the chemical bond, in thermody- 

 namics, leading to a better understanding of the dynamics of chemical re- 

 actions inside the plant; the magnificent advances in spectroscopy; and many 

 others; but I would be much amiss if I did not specifically enumerate high- 

 polymer chemistry. It was again a plant physiologist, Sponsler, who opened 

 the door to this field by his interpretation of the X-ray-diffraction pattern of 

 cellulose. The more we come to know about the living system, the more we 

 come to the conclusion that life is intimately linked with high polymers and 

 macro-molecules: proteins, nucleic acids as functional units, cellulose and 

 pectin as structural units, starch and inulin as energy storage. 



It is not only the basic sciences which have furthered plant physiology. Cell 

 physiological studies carried out mainly by zoologists have provided a basis 

 for understanding of the plant cell as well. Plant pathology has provided 

 plant physiologists with a magnificent experimental material, the crown gall. 



