UPWARD TRANSPORT OF NITROGEN 55 



There are no extensive data showing the extent of 

 transport into and export from leaf tissues, but Chibnall 

 (1923), basing his calculations chiefly on the fresh weight 

 basis, claimed a diurnal transport of from 2 to 4 per cent, 

 or more, of nitrogen. He also cites data from others who 

 claim a diurnal transport. Maskell and Mason (1929o), 

 expressing the fluctuations as percentages of the mean 

 content, found about 10 per cent fluctuation of nitrogen 

 on the fresh-weight basis and about 4,17 per cent fluctua- 

 tion on the residual dry-weight basis. (Subtracting the 

 standard deviations due to sampling there would be 

 respectively 8 and 2.75 per cent.) In a second series they 

 found diurnal variations amounting to about 16 per cent 

 on the fresh- weight basis and 14 per cent on the residual 

 dry-weight basis. Even accepting one of the lower figures, 

 that an amount equal to 4 per cent of the total nitrogen 

 of the leaf is transported from the leaf each night, then, if 

 the final amount has not changed, at the end of 25 days, 

 an amount equal to the total amount present at the end 

 has been transported from the leaf. This would greatly 

 increase the differences between the analyses of the ringed 

 and check stems, for little or none would be lost from the 

 leaves of the ringed stems. If nitrogen is removed from 

 the leaves during the day also — and Maskell and Mason 

 (1929a) claim a greater transport by day than at night — 

 then the total amount removed under the conditions here 

 assumed would be at least twice the amount actually found. 

 This would mean that the real difference between the amounts 

 moving through the check stems and the ringed stems is much 

 greater than the actual difference found by analysis. Under 

 such conditions it would seem that the differences in 

 transpiration rates could not account for the great differ- 

 ences in transport. 



At the time of performing the ringing experiments 

 reported in this section, I had assumed that, in order to 

 solve the problem as to what tissue is concerned in the 

 upward transport of nitrogen and ash constituents, all 

 that was necessary was to demonstrate an upward move- 



