THE METHOD OF MOVEMENT 169 



that this peculiar behavior of sieve tubes is abnormal and 

 is the result of injury due to cutting and loss of contents 

 by exudation. Calculations of rates of transport through 

 potato stolons, as well as rates of flow from cut phloem of 

 cucurbits, have led him to conclude that it is not possible 

 for solutions to flow through the pores of sieve plates at the 

 rate required for transport or actually observed in exuda- 

 tion. He suggests, therefore, that they must pass freely 

 across walls at all points. The finding of rapid exudation 

 from very young tips of shoots and roots, where differenti- 

 ated sieve tubes with visible pores are absent, has given 

 added impetus to this interpretation, although he seems to 

 disregard his observation that yoling sieve tubes do not 

 show this high permeability. 



A number of investigators have reported rapid exudation 

 from young undifferentiated tissues when these are cut 

 into. Sachs (1887, p. 362) had observed the exudation 

 of sap from the cut surface of turgid parenchyma and 

 remarked on the fact that the amount of exudate was so 

 great that it could not all have been contained in the cells 

 that were cut open but must have come from cells at some 

 distance from the cut. He points out that this is not so 

 easily explained as the exudation from cut sieve tubes or 

 latex vessels, for in the parenchyma cells the fluid must 

 filter through the protoplasmic linings. Miinch (1930) 

 reports exudation from exposed cambium, though he has 

 assumed this was mostly water. Crafts (1931, 1932, 1933) 

 has observed ready exudation from immature cells near 

 the shoot and root tips of Cucurbita and Solarium in which 

 sieve tubes had not become differentiated. James and 

 Baker (1933) have observed similar exudation from the 

 cambial region of Acer pseudoplatanus, and explain the 

 bleeding, observable in many stems, as having originated 

 from the cambial and other immature cells as a result of 

 flow of cell contents according to the Miinch mechanism. 

 They claim the exudate does not come from the xylem as 

 is usually assumed. Miinch and his followers interpret 

 this flow as indicating a normal translocation flow through 



