UPWARD TRANSPORT OF NITROGEN 



59 



which he thinks demonstrate that nutrient salts are carried 

 chiefly through the xylem. He has ringed stems of grapes, 

 plum, and three varieties of raspberry. This was done 

 early in the spring before the new shoots had formed. At 

 the end of the growing season he has compared the total 

 nitrogen and total ash contents of the ringed stems, 

 including the new shoots and leaves that had developed 

 from their buds, with those of similar stems taken at the 

 beginning of the experiment before new shoots had formed. 

 Averages of his findings are presented in Table 11. 



Table 11. 



-Data from Clements Showing Increase of Nitrogen and 

 Ash of Ringed Shoots 



Plant 



Grape 



Plum 



Black raspberry 



Cuthbert raspberry . . 

 Columbian raspberry , 



No. 

 of stems 

 averaged 



Total ash 

 relative to 

 sample at 

 beginning* 



43.3 



4.3 

 7.0 



8.9 



* Clements calls this "increase" over the sample at the beginning. The increase, how- 

 ever, is less by one in each case. 



Since the final contents average from nearly 3 to nearly 

 44 times the amounts originally present, he concludes that 

 the xylem is chiefly concerned in transport. With the 

 exception of the grape, which he says is very well suited 

 for ringing experiments, the final amounts were from three 

 to nine times the amounts originally present. 



He criticizes my experiments partly on the grounds that 

 I had no checks at the beginning, but he had no checks at 

 the end. Actually in many of the experiments I reported, 

 I did have check samples taken both at the beginning and 

 again at the conclusion of the experiments. It is true 

 that in none did I include the entire twigs, stems, and 

 leaves, at both periods, but in several cases check leaf 

 samples were taken both at the beginning and at the end 



