74 GROWTH HORMONES IN PLANTS 



The rate of transport, about 10 mm. per hour, is much greater 

 than can be accounted for by diffusion. It is not influenced by 

 the length of the tissue through which it is moved, is very httle 

 affected by temperature, and is practically independent of the 

 concentration gradient. 



Amount of Transport. — In contrast to the rate of growth-sub- 

 stance movement, the capacity of transport, (i.e., the amount 

 transported per unit of time, sometimes called intensity of 

 transport) is inversely proportional to the length of the coleoptile 

 at 0°C., but at higher temperatures it appears to be independent 

 of the length of the portion of the organ in question. If the 

 original concentration of growth substance is increased, the 

 absolute amount does not increase in proportion to the con- 

 centration rise, and the "relative" amount of transport conse- 

 quently decreases. The effect of rising temperature on amount 

 of transport shows an increase up to an optimum at 30 to 40°C. 

 Thimann (1935a) has Hkened the movement of growth substance 

 to the transport of objects along a moving band; the band 

 travels at a constant speed so that the number of objects arriving 

 at the end per unit of time is independent of the length; if not 

 removed from the end, there is an accumulation (transport 

 against the gradient) (see also van der Weij, 1932). 



X Irradiation and Transport. — Recent experiments by Skoog 

 (1935) have shown that the movement of growth hormone in the 

 Avena coleoptile is not affected by moderate dosages of X irradia- 

 tion (30 Rontgen units per minute at 900 kv. and 3 to 4 milli- 

 amperes for 200 minutes and more) . 



Anaesthesia and Transport. — In a later paper, van der Weij 

 (1934) has shown that anaesthetizing with ether abolishes polar 

 movement and stops all transport beyond that which can be 

 accounted for by diffusion. This anaesthetic inhibition is 

 reversible within certain limits of ether concentration. Small 

 concentrations of the anaesthetic had no effect upon the normal 

 rate of the transport, but increasing concentrations of ether 

 decreased the amount of transport. The nonpolarized move- 

 ment of growth substance under conditions of complete narcosis 

 was attributed to diffusion in adhering water films outside 

 the living cell material. Van der Laan (1934) reported that 

 ethylene (0.005 to 0.0005 per cent of gas) had no effect upon the 

 transport but inhibited the formation of growth substance in 



