UPWARD TRANSPORT OF ORGANIC MATTER 43 



It would seem that these data offer convincing proof in 

 favor of the hypothesis aheady strongly suggested by 

 ringing experiments that upward as well as downward 

 transfer of solutes takes place chiefly through the phloem 

 tissues. It certainly eliminates the criticism that ringing 

 stops solute movement because it causes a plugging of the 

 xylem, for when cut no xylem remains and yet translocation 

 takes place, whereas when the phloem is cut, little or no 

 translocation takes place, even when it is demonstrated 

 that the remaining xylem is not plugged. It also eliminates 

 the criticism that the phloem seems inadequate as a chan- 

 nel, for, although calculations of rates of food movement 

 seem to demonstrate its inadequacy, these experiments 

 definitely prove that the phloem has carried the foods and 

 salts and was therefore adequate in these cases. A com- 

 parison of the merits and weaknesses of the various methods 

 used in determining the tissues concerned in translocation 

 is discussed in Chap. IV. 



Mason and Maskell (1928a, p. 242) suggest that the 

 poor shoot growth of the ringed shoots may have been due 

 to a blocking of the tracheae and that the better growth 

 of those with the xylem cut may have resulted from develop- 

 ment of new wood elements. They seem to have over- 

 looked the positive evidence supplied in the original paper 

 that the vessels were not plugged in the ringed stems and 

 that new vessels had not developed in those with the xylem 

 cut. They also remarked on the lack of significant differ- 

 ences between the two treatments in the dry weights of the 

 shoots of Philadelphus but note the difference in Rhus. 

 They must have overlooked the statement preceding the 

 table on page 580 of the original article which definitely 

 explains that in the Philadelphus material, the newly 

 developed leaves and the basal parts of all the shoots 

 except the ringed ones were removed, so that pieces of 

 approximately equal length and weight and having the 

 same proportion of young leaves were selected for analysis. 

 If all the newly developed tissues had been included, the 

 check stems and those with the xylem cut would have had 



