CHAPTER VII 



PLANT NUTRIENTS AND THEIR ABSORPTION 



Plants require for their nutriment water, carbon dioxide, oxygen, 

 nitrates (or other nitrogen carrying compounds), sulphates, phosphates, 

 salts of iron, magnesium, potassium and calcium. Though chemical 

 analysis of plant tissue shows that almost every clement may be found 

 in one plant or another, carbon, hydrogen, oxygen, nitrogen, phosphorus, 

 sulphur, potassium, magnesium, iron, calcium, chlorine, silicon, sodium, 

 aluminum and manganese are found in practically all plants. The 

 first ten of these are necessaiy for all the higher plants. Water, nitrogen 

 and all the mineral elements are absorbed by the roots from the soil. 

 Absorption by the leaves also occurs under certain circumstances but 

 ordinarily this process may be disregarded. The water relations of 

 plants have been treated in the previous section; the other plant nutrients 

 absorbed from the soil form the subject of this chapter. 



DISTRIBUTION OF ELEMENTS FOUND IN ASH 



The mineral constituents of plants, except a part of the sulfur, are 

 left as ash after the tissue has been burned. Some conception of the 

 amount and composition of plant ash may be derived from the analyses 

 of the wood, bark and leaves of the beech in Table 1. 



Table 1. — Ash Analyses of Wood, Bark and Leaves of Beech"* 



In Tissues of Different Kinds. — The data in Table 2 on the amount 

 and composition of the ash of apple trees, give an idea of the variations 

 that maj^ occur in the composition of different parts. The distribution 

 of ash in the apple tree at the time of leaf fall is shown in Table 3. The 

 ash percentage of bark is always many times that of the wood as Table 4 

 shows. The ash content of seeds varies from 2 to 6 per cent. Thus, 

 seeds of the chestnut contain 2.38 per cent, of ash, almonds 4.9 per cent, 

 and coffee 3.19 per cent.^ The composition of such ash appears from 

 data presented in Table 5. 



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