A. J. HAAGEN-SMIT 5 



number of routine analyses necessary for isolation of the actiye material. 

 Moreoyer, most of these problems require research budgets, which, in 

 the time of Fitting and long afterward, were extremely small. Fitting 

 makes special mention of the fact that he bought some of the orchids 

 himself. Finally, the borderline nature of the problem required the 

 cooperation of seyeral workers, and team work in science belongs to a 

 much later date. 



At about the time of Fitting's work, another field of plant physiology 

 dealing with phototropic and geotropic phenomena was rapidly develop- 

 ing. As early as 1880 it had been shown by Darwin (9) that some influence 

 is transmitted from the upper to the lower part in seedhngs when they 

 are exposed to one-sided illumination. Boysen-Jensen (7,8) showed in 

 19 13 that this stimulus can be transmitted through a gelatin layer by 

 cutting off the tips of Avena coleoptiles and pasting them on again with 

 gelatin. After one-sided illumination the curvature appeared not only 

 in the tip but also in the lower part. Boysen-Jensen was very cautious in 

 the explanation of this phenomenon and assumed that a concentration 

 change in the tip was responsible for this effect. 



Paal (48) in 19 19 demonstrated that the stimulus did not cross a 

 layer of cocoa butter, mica, or platinum foil, and that a tip placed on one 

 side of the coleoptile caused curvatures similar to those seen in photo- 

 tropic experiments. He postulated the existence of a diffusible correlation 

 carrier, a substance which is produced in the tip and moves downward. 

 Phototropic effects were explained by an interruption of the normal flow 

 of the substance through interference in its action due to some change 

 in the protoplasm. This clear formulation of a substance as the active 

 agent was an important step forward. 



Several unsuccessful attempts were made to collect the active material 

 from crushed coleoptiles until Went (63) showed that it diffused into 

 gelatin from living coleoptile tips. For the measurement of the growth 

 effect Went improved the technique introduced by Stark and Drechsel 

 (54). This made it possible to conduct the physiological experiments on 

 a quantitative basis, a prerequisite for the chemical isolation of the 

 growth substance. Because of the importance for all the subsequent work 

 let us briefly review this measuring method and its later modifications. 



For this test etiolated oat seedlings are used, from which, three hours 

 before testing, the tip is removed. After the primary leaf has been 

 detached from its base and a second decapitation has been performed, 



