THE METHOD OF MOVEMENT 219 



from that proposed by Miinch, and when the osmotic 

 concentration of the emptying tissue is less than that of the 

 receiving. 



Growth responses involving matters of regeneration and 

 dominance of the sort described in Sees. 41 and 42 have 

 often been ascribed to transport of special hormones. The 

 effects seem to be controlled in many cases by transport 

 or transmission through the phloem. If they are due to 

 transport of hormones, as often assumed, and since the 

 direction of movement is often not the same as that of 

 sugar movement, the evidence would point to transport 

 in both directions simultaneously. This would seem to be 

 in opposition to the ISIiinch or Crafts hypothesis. Miinch 

 (1932) assumes different growth substances to be concerned 

 in shoot growth and cambial growth, and suggests that 

 growth may also be partly controlled by inhibitors. Since 

 these growth substances seem to be transported through 

 the phloem and not always in the same direction as the 

 assimilates, he suggests that they do not move through 

 the sieve-tube lumen because, according to his hypothesis 

 the sieve-tube contents can move in but one direction 

 at a time. He points out that Went's suggestion (1932), 

 that they are carried in companion cells, is untenable 

 because companion cells are absent in conifers. He thinks 

 it probable that they are carried in the walls, as suggested 

 by Van der Wey (1932), while the mechanism and direction 

 of transport are controlled by their electrical charge. 

 There seems to be no clear-cut evidence, however, indi- 

 cating such movement along walls and both Van der Wey 

 and Miinch suggest the walls because they think moving 

 protoplasm is not concerned or that movement can be in 

 only one direction through the lumen. 



Studies on the translocation of hormones, viruses, and 

 fluorescein have been interpreted by several investigators 

 as indicating a unidirectional movement through phloem 

 and an outward transport only from mature leaves. Both 

 fluorescein and viruses seem to move only outward from 

 mature leaves even when darkened for varying periods, and 



