128 INORGANIC CONSTITUENTS OF PLANTS. 



common rain water, containing, of course, a certain quantity of in- 

 organic matter. 



The elementary bodies already mentioned, in various states of 

 combination, constitute the great bulk of plants. They occur in the 

 form of binary compounds, as water and oily matters ; ternary, as 

 starch, gum, sugar, and cellulose; quaternary, as glutin, albumin, 

 casein, and fibrin. The latter compounds seem to require for their 

 composition not merely the elements already noticed, in the form of a 

 basis, called Protein, but certain proportions of sulphur and phosphorus 

 in addition ; thus, albumin = 10Pr. + 1P + 2S; fibrin = 10 Pr. 

 + 1 P + 1 S ; casein = 10 Pr. + 1 S. The tissues, into the com- 

 position of ■which these protein compounds enter, are tinged of a deep 

 orange-yellow by strong nitric acid. These compounds are highly 

 important in an agricultural point of view, and the consideration of 

 them will be resumed when treating of the application of manures. 



Inorganic Constituents and their Sources, 



The consideration of the inorganic constituents of plants is no less 

 important than the study of their organic elements. The organic 

 substances formed by plants are decomposed by a moderately high 

 temperature ; they easily undergo putrefaction, especially . when ex- 

 posed to a moist and warm atmosphere, and few of them have been 

 formed by human art. Their inorganic constituents, on the other 

 hand, are not so easily decomposed ; they do not undergo putrefaction, 

 and they have been formed artificially by the chemist. 



The organic part of plants, even in a dried state, forms from 88 

 to 99 per cent of their whole weight. Consequently, the ash or 

 inorganic matter constitutes a very small proportion of the vegetable 

 tissue. It is not, however, on this account to be neglected, for it is 

 found to be of great importance in the economy of vegetation, not 

 merely on account of its entering directly into the constitution of 

 various organs, but also from assisting in the production of certain 

 organic compounds. Some of the lower tribes of cellular plants can 

 exist apparently without any inorganic matter. Thus Miilder could 

 not detect a particle of ash in Mycoderma vini, nor in moulds pro- 

 duced in large quantity by milk sugar. Deficiency of inorganic 

 matter, however, in general injures the yigour of plants, and it will 

 be found that, in an agricultural point of view, this requires par- 

 ticular attention— a distinct relation subsisting between the kind and 

 quality of the crop, and the nature and chemical composition of the 

 soU in which it grows. It has been shown, by careful and repeated 

 experiments, that when a plant is healthy and fairly ripens its seeds, 

 the quantity and quality of the ash is nearly the same in whatever 

 soil it is grown ; and that, when two different species are grown in 



