THE TRANSPORT OF GROWTH SUBSTANCES 77 



his "growth-retarding substance" was moved by protoplasmic 

 streaming. A rapid streaming of the protoplasm in the cells of 

 the coleoptile has been observed by Brauner (1922), Perry (1932), 

 Botteher (1934), and others. According to Went (1928a), the 

 rate of this streaming is of the right order of magnitude to serve 

 as an explanation for the rate of growth-substance transport. 



The longitucUnal movement of growth substance in Avena 

 apparently is not influenced directly by light (Boysen Jensen, 

 1933a). However, the effect of hght upon protoplasmic stream- 

 ing, the lateral displacement of growth substance, and tropic 

 curvature in Avena is well-known (Botteher, 1933, 1934; Went, 

 1928a; Boysen Jensen, 1933a). Botteher (1934) found that the 

 retarding action of different wave lengths of light upon proto- 

 plasmic streaming paralleled the phototropic effectiveness. 

 Furthermore, the supply of oxygen also has a marked influence 

 upon streaming (Botteher, 1935). 



Van der Weij (1932) questioned the significance of protoplasmic 

 streaming for transport of growth substance because, if proto- 

 plasmic streaming plays an essential part, the rate of movement 

 should be dependent upon the rate of protoplasmic streaming and 

 therefore upon the temperature. Since it was found that the rate 

 of transport is not changed by an increase in temperature, van der 

 Weij concluded that growth substance is not moved in the stream- 

 ing protoplasm but rather in the "resting" plasma membrane, 

 which was considered as "cell-wall substance in statu 7iascendi." 



It may be premature to draw far-reaching conclusions from 

 van der Weij 's investigations, but it would appear that the trans- 

 portation of growth substance is connected in some way with 

 living processes. Botteher (1934) has found that in young 

 coleoptiles of Avena the rate of protoplasmic streaming between 

 17 and 35°C. is influenced very little by the temperature. How- 

 ever, the intensity of streaming (i.e., the amount of protoplasm 

 in actual rotation) increases with temperature, 30°C. being 

 optimum (Botteher, 1934). F. A. F. C. Went (1935) has pointed 

 out the existence of similar values for the Qio of protoplasmic 

 streaming (Botteher) and growth-substance transport (van der 

 Weij) between 16.5 and 24°C. Since the intracehular movement 

 of the hormone by protoplasmic streaming would be considerably 

 more rapid than its observed transport velocity in plant organs, 

 the conclusion seems to follow that cell-to-cell transport must 



