INDIVIDUAL ELEMENTS 157 



face layers to produce 5,000 to 55,000 heavy corn crops if the supply is not 

 replenished and if it becomes available gradually. ^'^^ All the chemical 

 analyses of fruit soils given in the chapter on Orchard Soils indicate that 

 the danger from calcium starvation in the orchard is very remote. In 

 all probabihty the amounts of calcium found in plant tissues are often 

 much in excess of their nutritive requirements. There is no doubt that 

 calcium is of use in the elimination of poisonous products of catabolism, 

 such as oxalic acid, but it seems not at all unlikely that in many cases the 

 oxalic acid is produced as a means of rendering a surplus of calcium 

 insoluble. 



Many orchard fertilizer experiments have been conducted in which 

 lime has been used, either alone or in combination. The results attending 

 these experiments have been variable, but on the whole negative in 

 character. Certainly there is no clear evidence available to show that 

 liming the soil is of any direct benefit to the trees. It has been pointed 

 out that applications of lime may aid nitrification in the soil and may be 

 of use to other cultures that are being grown in the fruit plantation and 

 thus -indirectly to the trees; on the other hand, it has been shown also 

 that they may have a very deleterious influence on tree or vine growth and 

 these deleterious influences are of sufficiently frequent occurrence in 

 actual field practice to suggest caution. It may be recalled that the 

 purpose for which lime is generally used with field crops, namely the 

 correction of soil acidity, needs but little consideration in deciduous fruit 

 production. 



OTHER MINERAL ELEMENTS 



Beside the elements already discussed, there are others that are of 

 universal occurrence in plants, though they are generally considered to be 

 unessential. However, copper which occurs in very small amounts 

 in plant tissues is considered by Maquenne and Demoussey''^ to be an 

 essential element. 



Silicon. — Silica is universally present, though the amount is very variable. 

 In leaves, for example, it may be present in mere traces or it may constitute 80 

 per cent, of the ash. In grape leaves amounts ranging from 1.61 per cent, to 

 39.44 per cent, have been found, the amount usually increasing with age.** 

 Table 53 illustrates this point. 



T.VBLE 53. — Grams of Silica in 100 Branches of Horse-chestnut and Their 



Leaves ^ 



