THE METHOD OF MOVEMENT 189 



Since their data are expressed only as percentages of 

 dry weight, there is no way of knowing what the actual 

 concentration gradients were. They assume that the 

 percentage of dry weight indicates actual concentration 

 gradients and imply a diffusional mechanism for transport. 

 They say that Brasse in 1886 pointed out that if sugar 

 moves as sucrose it must move contrary to ordinary 

 laws, for the concentration in the receiving cells is higher 

 and therefore movement would be expected in the opposite 

 direction. Although Davis, Daish, and Sawyer them- 

 selves, imply a diffusion mechanism for transport and their 

 data show a rather steep gradient for hexoses, they make 

 no comment on the fact that the concentration gradient 

 for these hexoses leads from the storage organ to the leaf 

 and not in the direction of assumed movement. The 

 sucrose gradient is less steep but does lead in the proper 

 direction, that is toward the storage organ, and the con- 

 centrations show only sUght daily or seasonal fluctuations. 

 The hexoses, on the other hand, fluctuate greatly both with 

 time of day and with season. Although they conclude 

 that hexose is the translocation sugar, it is conceivable 

 that the sugar was actually being transported as sucrose 

 along a positive diffusion gradient and the variations in 

 hexoses merely indicate temporary accumulation and 

 depletion in nonconducting tissues. 



If the percentages of dry weight indicate the relative 

 actual concentrations, the total osmotic concentration due 

 to carbohydrates becomes greater at greater distances from 

 the leaf, for although total sugar, as percentage, varied 

 only sUghtly between upper and lower parts, the hexose 

 increased markedly at greater distances from the leaf 

 blade. This would be contrary to the requirements of 

 the Miinch hypothesis. The hexose gradient is also con- 

 trary to the requirements of the diffusion hypothesis. The 

 sucrose gradient within the midribs and stalks, however, 

 seems in agreement with the diffusion hypothesis. The 

 leaf concentrations, on the other hand, are low and the 

 concentration in the receiving organ is not given. Since 



