Expanding Concepts 17 



turgor, and caused in his opinion the bending toward light. The re- 

 sults of the decapitation experiments he considered explainable on 

 the basis that decapitation opened the veins and increased water loss. 

 It is a little difficult to understand how so able a physiologist as 

 Priestley could have read the results of Darwin, Boysen Jensen, and 

 those who followed, and then could propose an explanation for the 

 phototropism of coleoptiles which so obviously was inadequate and in 

 error. 



The final and indisputable proof of the existence of potent growth 

 regulators for plants was given by F. W. Went (25), son of the botanist 

 F. A. F. C. Went, whose laboratories in Utrecht had for many years 

 been concerned with a careful and extended study of phototropism. 

 Went demonstrated that active material would diffuse from a coleop- 

 tile tip into a block of gelatin which would then act as the tip itself 

 did. From the diffusion rate he calculated the molecular weight of 

 the compound to be in the vicinity of 376. It was thermostable and 

 withstood drying. In addition to the final and convincing proof of 

 the existence of a growth regulator, the great contribution made by 

 Went was his method of quantitative determination of the growth 

 regulator by using gelatin or agar blocks placed laterally on the de- 

 capitated base of oat coleoptiles under controlled conditions. 



A preliminary report of the experiments of Fritz Went was made 

 by his father in a notable address on Plant Movements at the Inter- 

 national Congress of Plant Sciences at Ithaca, New York, in 1926 (24). 

 I well remember hearing rumors that evidence would be presented 

 for a thermostable, water-soluble substance involved in phototropism 

 and the skepticism freely expressed by many of my colleagues. 



However, from this time on, a widening circle of investigators 

 busied themselves with the problem. The discovery of a wide range 

 of synthetic compounds which have effects similar to those of the na- 

 turally occurring auxins has engaged the attention of many investi- 

 gators, among others those at the Boyce Thompson Institute. The 

 application of the auxins and similar compounds to the induction of 

 root formation, weed control, prevention of preharvest drop of ap- 

 ples and other fruits, increasing fruit set, inducing seedless fruit for- 

 mation, thinning of fruit, regulating flowering, increasing fruit size, 

 and hastening ripening has become increasingly important. 



Although the practical applications of the auxins are not to be 

 underestimated, the great importance of their discovery was to give 

 impetus to the concept that minute amounts of naturally occurring 

 organic substances could profoundly influence plant growth and de- 

 velopment. 



One of the few comforts of reaching what some charitably refer 



