102 PHYTOHORMONES 



There is thus sufficient parallelism to suggest that proto- 

 plasmic streaming could account for the high velocity and 

 capacity of auxin transport, though it cannot, of course, 

 account for the polarity. The latter might perhaps be lim- 

 ited to the passage from cell to cell. Alternatively, the re- 

 lation may not be causal, but both transport and streaming 

 may be dependent on the same underlying cause. 



Although the transport of auxin is not readily comparable 

 with that of other organic substances in plants, it may be 

 mentioned, firstly, that Kok (1931, 1932) failed to find any 

 influence of protoplasmic streaming on the transport of 

 lithium or of caffeine. In the second place, if the transport 

 of auxin were comparable with that of fluorescein within 

 the tissues, then the above theory would be almost certainly 

 discredited by the observations of Schumacher (1936). 

 Among a number of interesting experiments made with the 

 fluorescence microscope, he has observed that in hair-cells 

 of Cucurbita the fluorescein moves strictly polarly towards 

 the tip of the hairs. At the same time the protoplasm was 

 observed to be in vigorous rotation, and the movement of 

 the fluorescein continued independent of it. The dye ap- 

 peared to move through the cross walls as readily as in the 

 cells, and he suggests that the movement takes place in 

 some way along the wall itself. In this connection Mangham 

 (1917), Van den Honert (1932), and Sollner (1933) have sug- 

 gested a mechanism for the transport of organic substances 

 which fits in very well with the observations and might 

 explain some aspects of auxin transport. 



If at an interface between two liquids, such as ether and 

 water, a third substance which is absorbed at this interface 

 be added, it will move along the interface with a velocity 

 of up to 3 cm. per second. If the arrangement is such that 

 this third substance reacts at the other end of the interface, 

 considerable amounts of it may be so transported (see 

 Figure 39). Van den Honert achieved this result by using 

 potassium oleate as the third substance, and allowing it to 

 react with HCl at the other end of the interface. This 



