INDIVIDUAL ELEMENTS 



143 



during the period of fruit bud differentiation there is a marked increase which is 

 particularly pronounced in spurs differentiating fruit buds. Phosphorus accu- 

 mulation in the fall is well marked, especially in productive spurs. 



In bearing spurs there is a considerable increase in phosphorus during 

 blossoming, indicating that these organs draw upon a supply of stored phos- 

 phorus, which may be assumed, by analogy with nitrogen, to be in the bark. 

 Moreover, the phosphorus content of bark is at a maximum in the spring. 



In Fruit. — As soon as the fruit begins to develop, the phosphorus content 

 of the bearing spur decreases. At this time the spur probably is supplying the 

 young fruit with phosphorus, which accumulates, to a considerable extent, in 

 fruits and seeds. This increase is illustrated by the figures in Table 28 showing 

 the amounts in ripening grapes. 



Table 28. — Grams of Phosphorus in 1,000 Berries of the Grape*'* 



July 27 0.169 Sept. 17 0.434 



Aug. 9 0.315 Sept. 28 0.550 



Aug. 17 0.262 Oct. 5 0.619 



Aug. 28 0.206 Softening Oct. 12 0.455 Fully ripe 



Sept. 7 0.373 Oct. 22 0.320 Rotten 



In Various Tissues of Trees- of Different Ages. — The percentages and absolute 

 amounts of phosphorus in the tissues of apple trees of various ages is shown in 

 Table 29. In general the new growth and the leaves, even at the time of leaf 

 fall, are richest in phosphorus, the fruit next, then the roots; the trunk and older 

 branches have the least. 



Table 29. — Phosphorus Content of Apple Trees of Various Ages 

 (1 lo 9 computed from Thompson,^^^ 13 and 100 from Roherts,^^'' 30 from Van Slyke^^°) 



Of particular interest is the comparison of the absolute amounts of phosphorus 

 in the fruit and leaves with the nitrogen content of these tissues. In a 30-year 

 old tree in full bearing more phosphorus is lost with the crop of fruit than falls 

 with the leaves, even if it be assumed that 25 per cent, of the original amount was 



