216 TRANSLOCATION IN PLANTS 



should be markedly influenced by temperature because 

 the rate of protoplasmic streaming is greatly influenced 

 by temperature, whereas actually the velocity seems 

 entirely uninfluenced by temperature, while intensity is 

 greatly influenced. He points out that the growth sub- 

 stance seems to be transported by a mechanism analogous 

 to a carrier belt which moves at constant speed, the 

 carrying capacity of which, however, is greatly influenced 

 by temperature. He suggests that capillary electrical 

 forces somehow account for transport. Points favoring 

 this are that the growth substance is known to be a weak 

 acid, bearing an electrical charge, and therefore will be 

 moved by electrical forces ; evidence presented by a number 

 of investigators indicates that living plant cells maintain 

 an electrical polarity, and Kogl (1933) has found that 

 externally applied potentials alter the speed of the hormone 

 movement. Transport of growth substance under such 

 conditions may be a type of electro-endosmose or cata- 

 phoresis. With such an assumption, it is understandable 

 why velocity is almost independent of temperature, while 

 intensity is so strongly influenced, because the electrical 

 charge would be independent of temperature while the 

 effective path may be strongly influenced by temperature. 

 The path of transport he suggests to be the plasma that 

 permeates the walls of the parenchyma cells as well as the 

 nonmoving protoplasm which lies at the surface of the 

 wall. This cell-wall plasma, according to his opinion, is 

 continuous from cell to cell through young walls and the 

 connection is not restricted to the plasmodesma. He 

 considers that the movement is not a mass flow of the sort 

 proposed by Crafts but one dependent on electrical charge 

 and potential. 



If the findings and suggestions of Van der Wey for the 

 transport of this growth substance are confirmed, it would 

 seem that living cells may transport different substances 

 along different paths and perhaps by different mechanisms. 

 For example, Schumacher (1933) gives strong evidence 

 that the velocity of transport of fluorescein is greatly 



