INDIVIDUAL ELEMENTS 



141 



more thoroughly than its nitrogen, withdrawing it more completely from tissues 

 that are exfoliated and either using it immediately in tissue building or storing it. 



Table 25. — The Phosphorus Content of Leaves^^* 

 (In percentages of dry weight) 



Apple 



May 9, 14, 18 



June 22 



Aug. 29 



Sept. 30, Oct. 2, 15 



0.566 

 0.245 

 0.207 

 0.126 



Pear 



0.595 

 0.181 

 0.177 

 0.069 



Cherry 



0.602 

 0.302 

 0.329 

 0.273 



Plum 



0.510 

 0.305 

 0.289 

 0.197 



The absolute amounts of phosphorus in leaves of various ages are shown in 

 Table 26. As with nitrogen, the total amount of phosphorus in the leaf is low at 

 first, despite the high percentage, becau.se of the small size of the leaf. It then 

 increases as the leaf grows, reaches a maximum and finally decUnes, the dechne, 

 however, coming only a short time before abscission. 



T.\BLE 26. — Grams of Phosphorus in 100 Le.wes'^* 



Apple 



Pear 



Cherry 



Plum 



July 14 



July 31 



Aug. 18, 21 



Sept. 3, 4, 6 



Oct. 23, 27, 29, Nov. 4. 



0.036 

 0.043 

 0.034 

 0.034 



0.072 

 0.069 

 0.068 

 0.061 

 0.061 



0.054 

 0.049 

 0.049 

 0.044 



In the work from which this table is computed the possibihty of loss of nutri- 

 ent elements by cUmatic agencies was considered. Le Clerc and Breazeale'*^ 

 caUed attention to the possibility that plant tissue may lose considerable amounts 

 of mineral constituents through the dissolving action of rain. In this way 

 apple leaves attached to the branches lost 3 per cent, of their nitrogen, 

 25 per cent, of their phosphorus, 18 per cent, of their potash. and 6 per cent, of 

 their Ume simply by washing in water. This indicates that considerable amounts 

 of soluble substances exuded from the surface may be washed off the leaves during 

 the period between the formation of the abscission layer and the time of actual 

 leaf fall. 



In Branches, Trunk and Roots. — The percentage of phosphoric acid (P2O5) in 

 the ash of sap-wood is usually higher than in bark ash; for example, in the pear it 

 has been recorded as 12.62 per cent, in the sap-wood, as 2.98 per cent, in the bark 

 and in the grape 7.625 per cent, in the sap-wood and 4.705 per cent, in the bark.«* 



This does not mean, however, that the bark contains less phosphorus than the 

 sap-wood, for as has been pointed out, the total ash content of wood and 

 especially sap-wood is much less than that of bark. The figures indicate that 

 though the sap-wood contains relatively large percentages of phosphoric acid, in 

 the pear and grape at least the bark contains larger absolute amounts. 



