UPWARD TRANSLOCATION OF AIINERAL SALTS 495 



upward transport of mineral salts occurred even through stems from which 

 the phloem had been removed. 



While there is thus considerable evidence which indicates that upward 

 translocation of mineral salts occurs principally through the xylem, the work 

 of other investigators points to the diametrically opposite conclusion, i.e. that 

 the phloem is the main path of mineral salt transport. 



The results of a number of experiments by Curtis (1935) support this 

 view. The data from one of these are summarized in Table 47. 



TABLE 47 EFFECT OF RINGING ON INCREASE IN NITROGEN AND ASH CONTENT BY LEAVES OF 



PRIVET {Ligustrum sp.) (data of curtis, 1935). each figure is the average per 



STEM OF 12 SEPARATE DETERMINATIONS 



Area of leaves, dm.-. . 



Dry weight, g 



Total nitrogen, mg.. . 

 Nitrogen, mg. per 



dm.- 



Nitrogen, mg. per g. 



dry weight 



Total ash, mg 



Ash, mg. per dm.^. . . 

 Ash, mg. per g. dry 



weight 



Check 



Aug. 25 



0.956 

 1. 130 

 16.43 



17.07 



14.41 



85.4 



92.0 



77.8 



Oct 3 



and 4 



1 . 104 

 1-376 

 34-51 



24.81 



139-9 



in-j .1 



lOI .4 



Ave. 

 increase 

 per cent 



16.6 



22.9 



115. 9 



82.4 



67.6 

 61. 1 

 38.8 



30.8 



Ringed 



Aug. 25 



0.902 



14. 10 



16. 14 



13.90 



79.8 



91.9 



79-8 



Oct. 3 



and 4 



1 .017 

 1 .696 

 17-38 



16.88 



10. 13 

 95.2 



95-1 



57-1 



Ave. 

 increase 

 per cent 



12.9 

 66.2 



22.7 



6.5 



-25.5 

 20.7 



3-8 

 — 27.2 



o 



en tn 



■■" .E '-^ 

 y S rt 



u. u '^ 



'^ r- >*. 



CU .- O 



3-7 



-43-3 



93-2 



75-9 



105-3 

 40.4 



35-0 

 58.0 



This experiment was performed upon privet stems after shoot elongation 

 and xylem formation had ceased for the season. One leaf from each pair 

 was removed at the beginning of the experiment (August 25) from 24 stems. 

 Half of these were ringed so as to remove the phloem and leave the xylem 

 intact; the other half served as checks. The remaining leaves were collected 

 on October 3. Each set of leaves from each stem was analyzed for nitrogen 

 and total ash. 



These data seem to indicate that more nitrogen and inorganic solutes 

 were transported through the intact than through the ringed stems, and 

 appear to point definitely to the phloem as the principal route of transport. 

 Since ringing of stems invariably seems to result in a reduction in the trans- 

 spiration rate the objection might be raised that the mineral salts are being 



