62 6 WENT 



marized in Crocker and Barton's book. As in the rest of the world, the 

 numerous seed-testing laboratories have contributed very little to our theoreti- 

 cal insight of germination problems. An exception to this general rule should 

 be made for the investigations of both the Tooles at the U.S. Department 

 of Agriculture, now joined by Hendricks and Borthwick in connection with 

 the light sensitivity of germination of lettuce. 



Fruit physiology, being of commercial importance in relation to shipping 

 conditions and storage, has received much attention, as indicated by the 

 studies of Harvey in Minnesota, Smock at Cornell, and most recently Biale 

 at U.C.L.A., who has investigated especially the respiration behavior of fruits 

 in connection with ripening: establishing the so-called climacteric in lemons, 

 avocados, and a few other fruits. 



Probably no other problem can claim such a high degree of American 

 stimulation as that of flower induction. In their classical paper in 1920, 

 Garner and AUard demonstrated that the length of daily illumination con- 

 trolled the flowering behavior of a large number of plants, particularly annuals. 

 From a theoretical point of view this discovery was of the greatest importance, 

 because a morphogenetic process could thus be controlled experimentally. It 

 is gratifying that the U.S.D.A., in whose laboratories this work was started, 

 has continued its investigation in Beltsville under the direction of Borthwick, 

 Parker, and Hendricks. But now everywhere in the United States and the 

 rest of the world, photoperiodism is one of the most important research sub- 

 jects. And there is hardly a Department of Horticulture where the flowering 

 of flower crops is not being controlled by photoperiodic treatments. 



In the same year, 1920, another important paper appeared on control of 

 plant development, namely, one by Coville, in which he showed that dor- 

 mancy of leaf and flower buds in deciduous plants could be broken by keeping 

 the plants in the cold for several months. Soon afterward it was found that 

 this chilling treatment can also induce flowering in many plants, such as 

 sugar beets. Now chilHng of seeds or plants (sometimes called vernalization) 

 provides an experimental tool for research in plant development of equal 

 importance to day-length treatments. 



The pioneer investigators in the field of plant hormones and growth sub- 

 stances in this country were Dolk and Thimann at Cal Tech. When it became 

 clear to what extent plant development could be controlled by chemical means, 

 using auxins and chemically related compounds, suddenly from 1935 studies 

 on plant-growth substances became very popular research subjects; and when 

 it turned out that chemically related compounds were highly effective weed 

 killers, all stops were pulled. To enumerate the principal investigators in the 

 plant-growth-substance field would lead to a roster of American plant physi- 

 ologists. Very active groups in this field are at the California Institute of 

 Technology, the Boyce Thompson Institute of Plant Research, the U.S.D.A. 

 Agricultural Research Center in Beltsville, the Army Chemical Corps, the 



