INDIVIDUAL ELEMENTS 147 



marked difference in this respect between potassium and phosphorus or nitrogen 

 suggests a corresponding difference in their utihzation by the plant. Possibly 

 the elaboration of potassium is not localized in the leaf. 



Though the amounts of potassium removed from the leaves before they fall 

 seem small in comparison with phosphorus, there is none the less evidence of 

 potassium storage in the branches. Table 35 gives data showing the withdrawal 

 of potash from the leaves into the branches. 



Table 35. — Grams of Potash in 100 Branches of the Horse-chestnut and 

 Their Leaves* 



Branches Leaves 



July 29 1.763 



Sept. 11 2.249 



Oct. 14 2.575 



Nov. 16 I 2.671 



18.876 

 14 . 236 

 13.400 



In Branches, Roots and Trunks. — The leaves lose more potassium than can be 

 accounted for by the gain in the branches on which they were borne, indicating 

 that considerable amounts of potash are washed from the leaves by rain. The 

 relative amounts of potash in the ash of sap-wood and bark resemble those of 

 phosphorus. In one series of determinations the ash of the sap-wood of the pear 

 was 22.25 per cent, potash, of the bark 6.2 per cent.; the sap-wood ash of the 

 apple was 16.19 per cent, potash, the bark ash 4.93 per cent, and the sap-wood 

 ash of the grape was 20.84 per cent, potash, the bark ash 1.77 per cent.^^ In 

 the sap-wood ash there is more potash than any other element except calcium ; in 

 the bark the potash content is lower and the calcium content higher, but the 

 absolute amount in the bark is probably greater than in the sap-wood on account 

 of the bark's higher ash content, as has been pointed out in the discussion of 

 phosphorus. 



Table 36, showing seasonal variations in the potash content of the root, trunk 

 and branches of a 7-year old apple tree, gives additional evidence of the storage 

 of potassium in the branches. 



Apparently potassium is stored in old branches to a relatively greater extent 

 than nitrogen or phosphorus, for in the 3-, 4- and 5-year old branches the potash 

 content reaches a minimum in May though the 1- and 2-year old branches have a 

 high content at that time and do not reach a minimum until later. The young 

 roots and branches are richer in potassium, as in phosphorus and nitrogen, than 

 the older parts of the tree. 



Potassium probably is stored in both bark and sap-wood. The layers of 

 bark nearest the cambium are richest in this element. Furthermore, the young 

 bark of the oak, horse-chestnut and walnut contains more potash in percentage 

 of total ash at the time of greatest vegetative activity in the spring than later in 

 the season. ^2 Similar seasonal differences oc(iur in the potash content of the sap- 

 wood of these trees, while the heart-wood not only contains considerably less but 

 its content is subject to much smaller fluctuations." Weber^^^ found that in 

 beeches producing many seeds, the sap-wood was particularly rich in potash 



