152 FUNDAMENTALS OF FRUIT PRODUCTION 



Iron usually constitutes 1 to 4 per cent, of the leaf ash. Grape leaves have 

 been known to have an exceptionally high figure, 10.20 per cent." The absolute 

 iron content of leaves increases with age, though the percentage composition of 

 the leaf remains fairly constant. 



Table 43. — Iron Oxide Content of Beech Leaves"^ 

 (In percentage of total ash) 



May 16 0.8 



July 18 1.4 



Oct. 15 1.3 



The ash of bark ranges from 0.2 to 3 per cent, of iron, the amount often 

 increasing with age; for example 0.2 per cent, has been found in the apple and 

 2.545 per cent, in the grape.^^^ Wood ash has but little iron, usually from 0.1 to 

 0.8 per cent. — 0.16 per cent, in the pear, 0.42 per cent, in the apple and 0.635 per 

 cent, in the grape.*^^ Exceptionally high figures have been found in the olive, 

 2.11 per cent, of the ash, and in the orange, 3.08 per cent.*" 



Table 44. — The Iron Oxide Content of Fruits*'* and Seeds^* 



(In percentages of total ash) 



Fruits Seeds 



Banana 1 . 46 Grape . 37 



Plum 2.54 Almond 0.55 



Apple 1 . 40 Walnut 1 . 32 



Pear 1.04 Coffee 0.65 



Orange . 46 Chestnut 0.14 



Grape 1.04 



Olive- .. . 0.72 



Iron is a constituent of practically all soils; furthermore it is always 

 found in quantities sufficient for the requirements of crop plants. How- 

 ever, in many cases it is held in the soil in a form unavailable to the plant; 

 consequently the plants may suffer because of iron starvation. Refer- 

 ence has been made to this in connection with the discussion of soil 

 reaction and more is said regarding the disturbances caused by a lack of 

 iron under the heading of Surpluses and Deficiencies. 



MAGNESIUM 



The most important organic compound containing magnesium is 

 chlorophyll. This element also occurs in organic combination in salts of 

 arable acid and in the globoid of aleurone grains. Some proteins are 

 thought to contain magnesium. Anthocyan pigments are complex 

 compounds with salts of magnesium, calcium or other metals. *^^ 



The absolute amount of magnesia in leaves increases as they grow 

 older. Thus 500 leaves of Platanus were found to contain 0.24 gram 

 of magnesia on June 13, 0.85 gram at the end of August and 0.69 gram 

 at leaf fall, showing a slight decline. ^^ However, there is not much change 

 in the percentage of magnesia in the total ash. On May 16, in beech 



