AUXIN TRANSPORT AND POLARITY 97 



becomes essentially a diffusion, the capacity becoming in- 

 versely proportional to the length of the section. This may 

 be compared with the transport at 0°, which also approaches 

 that of diffusion, but which, by contrast, maintains its 

 polarity. If the ether concentration used is just high enough 

 io make polarity disappear it will reappear on re-aeration 

 ("reversible narcosis ") . 



That the polar transport of auxin is as strict in the intact 

 plant as in cut sections follows from a number of considera- 

 tions. The strictly basipetal translocation of tropistic 

 stimulus mentioned above is a good example. The polarity 

 of root formation (XI B) and of cambial stimulation 

 (XIII B) are others. The experiments of Laibach and 

 Kornmann (1933a) also confirm it. They appHed small agar 

 blocks containing auxin to the outside of intact coleoptiles 

 at different distances from the tip. The resulting curvatures 

 were always below, never above, the block. However, Snow 

 (1936) finds that if relativel}' high concentrations of auxin 

 in lanoline are applied to the outside of coleoptiles, curva- 

 tures occur above the paste; this result is most marked if 

 the paste is applied to the narrow side (c/. above), and is 

 very slight and slow in beginning if applied to the broad side. 

 It is thus largely due to transport upwards in the tran- 

 spiration stream. 



The same polarit}^ of transport appears to hold in other 

 tissues, such as Elaeagnus stems (van der Weij, 1933a), 

 Raphanus hypocotyls (van Overbeek, 1933), Vicia Faba 

 stems (Thimann and Skoog, 1934), Lupinus hypocotyls 

 (Dijkman, 1934), Coleus stems and growing petioles (Mai, 

 1934; Gouwentak and Hellinga, 1935), Nicotiana leaf- veins 

 (Avery, 1935), Pisum stems (u), and Salix stems (Alichener, 

 u) ; apparently, however, it does not hold in roots (see IX C). 



Earlier workers on geotropism have found that plants 

 which are inverted after being placed horizontally give 

 greater geotropic curvatures than those which are placed 

 upright after the same geotropic stimulation (''geotonic 

 effect"). Since the geotropic reaction is now explained in 



