158 FUNDAMENTALS OF FRUIT PRODUCTION 



Bark ash usually contains less than 2 per cent, of sihca; for example, 0.4 per 

 cent, in the pear and 0.6 per cent, in the apple. ^* The ash of grape bark has been 

 shown to contain 14.3 per cent. siUca.^ Wood ash usually contains less than 

 3 per cent, of silica; for example, 0.3 per cent, has been recorded for pear wood, 

 1.65 per cent, for apple wood and 2.8 per cent, for grape wood.^'' The ash 

 of olive wood has been found to contain as much as 14.23 per cent, silica. ^^ As a 

 rule the heart- wood contains a higher percentage than the sap-wood. 



Fruits contain silica in amounts shown in Table 54. The seed usually con- 

 tains less, as the same table shows, though a trace at least is always present. 



Table 54. — The Silica Content of Fruits^'' and Seeds" 



(In percentages of total ash) 



Fruits Seeds 



Pineapple 5 . 77 Chestnut 1 . 54 



Banana 5.93 Grape 1 . 04 



Fig 2.34 Coffee 0.54 



Plum 3.15 Cocoanut . 50 



Apple 4.32 Walnut Trace 



Pear 1.49 



Orange . 44 



Grape 1 . 00 



Olive 0.65 



SiUcon usually is associated with the cell wall and sometimes confers strength 

 and stability on a plant tissue. However, the strongest and hardest of plant 

 materials are often of very nearly pure cellulose ; hence, a lack of silicon does not 

 necessarily involve mechanical weakness of mature tissues. 



Sodium. — Sodium also is of universal occurrence in plant tissues. Leaves 

 usually contain 1 to 3 per cent. Table 55 indicates the seasonal variation in 

 absolute amounts in five hundred Plalanus leaves. 



Table 55. — The Seasonal Variation in Soda Content of Platanus Leaves" 

 (Grams in 500 leaves) 



June 13 0.3152 Oct. 8 0.2898 



May 15 0.4187 Oct. 24 0.2439 



Aug. 22 0.4299 Nov. 5 0.2273 



Sept. 7 0.5641 



Bark and wood ash usually contain but little soda, 3.495 per cent, having been 

 recorded in the ash of apple bark and 0.27 per cent, in that of grape bark.^^ The 

 wood of the sweet cherry has been known to contain as much as 10.13 per cent.^® 

 As a rule there is less soda in the ash of heart-wood than in that of sap-wood, 

 certain sap-wood records showing for the pear 1.84 per cent, soda; for the apple, 

 3.275 per cent, and for the grape, 2.06 per cent.«^ Fruits contain soda in the 

 widely varying amounts shown in Table 56. 



Table 56. — The Soda Content of Fruits ^^ 

 (In percentages of total ash) 



Pineapple 6.75 Apple 26.09 



Banana 26.27 Pear 8.52 



Fig 19.63 Orange 13.47 



Plum 9.05 Olive 7.53 



