ESSENTIALS OF PLANT 



21 



large part of the sulphur is volatilized was overlooked for a long 

 time. For example, the following results 1 were obtained: 



The result has been that the draft of the plant on the sulphur 

 in the soil has been decidedly under-estimated, and it is quite 

 possible that some soils may be deficient in sulphur. 2 



Variations in Ash. 3 The percentage and composition of the 

 ash of plants varies according to the kind of plant, the part of 

 the plant, the stage of growth, the variety of the plant, the soil, 

 the season, and other conditions. 



Seeds contain plant food stored for the benefit of the young 

 plant, and are less variable in composition than any other portion 

 of the plant. Although they contain comparatively small quan- 

 tities of ash, the ash is rich in the essential plant foods. The 

 pure ash is composed largely of phosphoric acid, from 30 to 

 50 per cent.; potash, about 30 per cent.; magnesia, about 8 to 

 15 per cent. Lime is present in comparatively small quantity, 

 and little or no silica is found, except in the case of oats or 

 similar plants where the husk or chaff is included in the analy- 

 sis. (See table below). Leguminous seeds appear to be richer 

 in potash and poorer in lime than the seed of cereals. 



Roots and tubers, which, like seeds, contain a reserve store of 

 material for the use of the plant, are also rich in valuable plant 

 food, though more variable in composition than seeds. Unlike 

 seeds, the ash carries considerably more potash than phosphoric 

 acid ; but, like seeds, it contains more magnesia than lime. 



Leaves of plants are very variable in composition. The ash 



1 Fraps, Jour. Am. Chem. Soc., 23, 199. 



2 Jour. Agr. Sci., i, p. 217. 



3 See Wolff, Ashen Analysen. Also Tollens, Exp. Sta. Record 13, 

 pp. 207, 303. 



