INDIVIDUAL ELEMENTS 



153 



leaves it was found to be 4.36 per cent.; on July 18, 5.63 per cent, and 

 on Oct. 15, 4.12 per cent.^^^ The magnesium, like the iron content, keeps 

 pace with leaf development; this increase may be associated with the 

 chlorophyll content of the leaf. However, there is some evidence that 

 magnesium is withdrawn to the branches from the leaves late in the 

 season. There are also indications of magnesium storage in the sap- 

 wood, which is slightly richer in magnesium than the heart-wood. Dur- 

 ing the spring, there is more rnagnesium in the sap-wood than at other 

 times. Weber found that in beeches producing many seeds, the sap-wood 

 was especially rich in magnesia and potash, as compared with trees 

 bearing few seeds. ^^^ The sap-wood ash of the pear has been found to 

 contain 3 per cent, magnesia, of the grape 4.4 per cent, and of the apple 

 8.49 per cent.^^ 



The magnesia content of bark ash decreases with age. In young 

 bark it is 3 to 8 per cent., as in the leaves; in old bark 2 to 5 per cent. 

 Thus the magnesia of pear bark has been found to be 9.4 per cent, of the 

 ash, while in the apple bark it is 1.5 per cent, and in grape bark 0.8 

 per cent.^^ The sieve tubes sometimes contain magnesium phosphate; 

 this may be a form of storage. 



As a rule fat-storing seeds are richer in magnesia than starchy or reserve- 

 cellulose seeds; in the almond, magnesia has been found to be 17.66 per cent, of 

 the ash, in the walnut 13.03 per cent., while in coffee {Coffea arabica) beans it is 

 9.69 per cent, and in chestnuts 7.47 per cent.^^ 



Table 45 shows that the leaves of fruit trees contain much more magnesium 

 than the fruit. In the apple the magnesia content of the fruit has been found to 

 be 0.10 per cent, of the dry weight; of the leaves 1.03 per cent, and of the new 

 growth 0.30 per cent.^"> 



T.\BLE 45. — Pounds of Magnesia in Parts of a Mature Tree'®" 



Table 46. — The Magnesia Content of Fruits*' 

 (In percentages of total ash) 



Pineapple 9 . 79 



Banana 9.21 



Strawberry 2 . 93 



Plum 4 . 69 



Apple 8 . 75 



Pear 5 . 22 



Orange 8 . 06 



Grape 2.61 



Olive 0.18 



