44 TRANSLOCATION IN PLANTS 



a higher proportion of leaves and older stems and the data 

 would have shown very much higher dry weights for the 

 check shoots and those with the xylem cut. 



Others have suggested that measurements of elongation 

 as used in these experiments and in those reported earlier 

 (1920a), are not safe measures of solute movement or 

 growth, for the elongation, it is said, may have been due 

 largely to water absorption. Those making such criti- 

 cisms, however, have evidently overlooked the fact that 

 in the original pubhcations (1920a, 1925) dry weights and 

 sugar contents were included with the length measurements 

 in several of the tables. Though these data were pre- 

 sented, no great emphasis was placed upon the dry weights 

 in the discussion because the data showed such close agree- 

 ment between measurements of elongation and those of 

 dry weight, and the differences between the ringed and the 

 others were so great that it was assumed the relationship 

 was obvious to anyone sufficiently interested to question 

 the interpretation. Emphasis was, however, placed upon 

 the fact that the dry weights, expressed as percentages of 

 fresh weights, of the ringed shoots were always lower than 

 those in the checks or in the shoots with the xylem cut. 

 It seemed hardly necessary to point out, what should be 

 an obvious fact that, if the lengths and fresh weights of 

 the ringed shoots were from one-half to one-tenth or less 

 of those of the others and they also had a lower percentage 

 dry weight, the actual dry weights themselves also must 

 have been lower. Therefore the greater shoot elongation 

 of the stems with the xylem cut could not possibly have 

 been due to mere water absorption and extension, for they 

 had a dry weight content often in excess of two to ten times 

 that of ringed shoots. 



Schumacher (1931) by first cutting the phloem and then 

 the xylem in the petioles of Pelargonium leaves has recently 

 demonstrated a removal of nitrogen from darkened leaves 

 when the xylem alone is cut, and a lack of removal when 

 the phloem is cut. 



