A. J. HAAGEN-SMIT VJ 



other plants. Wilhelm (72) introduced a test method using the response 

 of the parenchyma tissue which hnes the hollow stem of the Windsor 

 bean, and Wehnelt (62) developed a test using the lining of the kidney 

 bean pod. A drop of crushed tissue applied to this layer causes rapid 

 cell division, and a small intumescence about one to two millimeters 

 high appears. The height of this new tissue measured after 48 hours is 

 to a large extent proportional to the concentration of the wound hor- 

 mone. The beginning of the curve represents reactions nonspecific in 

 nature, such as the result from appUcation of water, strong sugar solu- 

 tions, and toxic substances. After fractionation of the bean pod juice, 

 the active material proved to be an a, /3-unsaturated dicarboxylic acid 

 of twelve carbon atoms (11). This i-decene-i,io-dicarboxylic acid has 

 been named traumatic acid, and is active in amounts as little as o.i 

 gamma in the bean pod. Since in growth a considerable expenditure 

 of building material as well as stimulatory substances are necessary, it is 

 not surprising that several cofactors can increase the activity of traumatic 

 acid. Most striking is the effect caused by glutamic acid, which enhances 

 the activity of the wound hormone about ten times. 



English (12) has prepared several analogues of traumatic acid, and 

 shown that the activity is confined to the dicarboxylic acids. Both 

 saturated and unsaturated acids are active, but the double bond, while 

 not essential, increases the hormone action. For example, decane-1,10- 

 dicarboxylic acid has only half the activity of traumatic acid. The 

 structure of traumatic acid seems to indicate that it is a result of the 

 breakdown of fatty acids or their derivatives such as lecithins and fats. 

 No efforts have been made to establish its origin, and there is no informa- 

 tion on its mode of action. 



Since the time that the hormone concept was introduced in plant 

 physiology considerable progress has been made. Some of the correlation 

 carriers have been isolated and their actions have been studied. Still 

 many of the hormones remain to be discovered, and in addition a great 

 number of new problems have appeared. In striving for simpHfication 

 deductions in this field are often based on the results of work on a variety 

 of plants all through the plant kingdom. These extrapolations have had 

 a stimulating effect on the development of the hormone field, but with 

 the increase in our knowledge it is evident that there are a large number 

 of individual problems which require special investigation. Consequently, 

 the complete picture of hormone action on plant growth will un- 



