214 TRANSLOCATION IN PLANTS 



about phloem necrosis and other abnormahties and it 

 may be their movement is unrelated to normal solute 

 movement. Furthermore the amounts transported are 

 probably minute in comparison with the transport of 

 carbohydrates, nitrogen compounds and mineral nutrients. 



Among the many investigations on special hormone-hke 

 substances there has accumulated a fair amount of litera- 

 ture deaUng with their transport. It is not within the 

 scope of this work to discuss these interesting contributions 

 further than to touch very lightly on a few of the more 

 recent papers in so far as they deal chiefly with transport 

 through living tissues. Went (1932) seems to accept the 

 Miinch hypothesis as satisfactory for explaining the trans- 

 port of sugars through the sieve tubes. The direction of 

 this transport, he agrees with Munch, is determined by the 

 pressure gradient which, in turn, is controlled by ability 

 to supply or remove osmotically active material. He 

 emphasized, on the other hand, that the transport of 

 various growth substances is more strictly polar. These, 

 he suggests, are electrically charged and are carried cata- 

 phoretically under the influence of an electrical potential 

 whose direction remains constant. Negatively charged 

 substances, like the growth substance of Avena coleoptiles, 

 move basally only, while positively charged substances 

 move apically only. He suggests that these substances 

 are probably carried in companion cells of the phloem and 

 not in the sieve tubes. The evidence offered^ however, is 

 very weak. Since their movement is polar, while sugar 

 movement seems not to be, and since their rate of move- 

 ment seems much slower than that of sugar, he concluded 

 these special substances are carried in other cells than the 

 sieve tubes, and since other functions of companion cells 

 are not definitely known they seem to him very likely to be 

 the path for this special transport. 



Van der Wey (1932) has reported some interesting experi- 

 ments deaUng with the transport of the growth substance 

 of Avena coleoptiles. He summarizes his findings very 

 much as follows: (1) Both the velocity (the distance of 



