INDIVIDUAL ELEMENTS 



135 



year and there is little evidence of accumulation in the fall; this may be associated 

 with the absence of fruit bud differentiation in these spurs. 



Bearing spurs are peculiar, however, in that their nitrogen content increases 

 after the buds have broken, though in all other tissues of spur-bearing trees it 

 decreases when the plant is in bloom. This indicates that though the vegetative 

 tissues use locally stored nitrogen with the result that their nitrogen content 

 decreases, the blossoming spurs draw on a general supply and latet- upon the new 

 supply of the current season with the result that their nitrogen content is aug- 

 mented up to the time of fruit setting. This reserve supply is located probably 

 in the phloem, for a marked decrease in the nitrogen content of bark has been 

 found in many plants.^" In Rhus elegans for example the bark has been found 



^s^r^ to z J| 



Fig. 12. — Nitrogen content of apple spurs in percentages of dry weight, bearing spurs 

 represented by continuous lines marked W , B and / for Wealthy, Ben Davis and Jonathan 

 respectively; non-bearing spurs shown by broken lines marked B and J; barren spurs 

 represented by dot-dash lines marked B and N for Ben Davis and Nixonite. {After 

 Hooker. ^°<^) 



to contain 1.52 per cent, of nitrogen in the winter and only 0.36 per cent, in the 

 spring. Similarly in the bark of Acer platanoides 26 per cent, of the stored 

 nitrogen disappeared from winter to spring; in the bark of the cherry 37.16 per 

 cent, and in the red beech 30 to 50 per cent, disappeared during shoot growth. 



The nitrogen that is moved from the bark into the blossoming spur passes on 

 into the developing fruit, so that in the biennially bearing spur the nitrogen 

 content decreases as long as the fruit is attached. Murneek^" has shown recently 

 that the total nitrogen content of apple spurs is proportional to the leaf area and 

 that it decreases as a result of defoliation. 



In Fruit. — Though the nitrogen of the fruit, measured in percentages of dry 

 weight, decreases throughout development on account of the increment in dry 

 matter, the absolute amount present increases continuously. Table 20 shows 

 the nitrogen content of apples in percentages of dry weight and in absolute 

 amounts. 



