212 Spontaneous Changes of Organized Ma'lcr. [April, 



As it regards the power which plants possess for obtaining 

 nitrogen, it is proper to remark (hat they differ extremely, one 

 class, for instance, being placed a' one extreme of a scale and 

 another at the other extreme: thus clover, or trefoil, possesses the 

 power of taking it from the atmosphere, or from a source inde- 

 pendent of the soil, and hence it will grow in sand destitute in a 

 great measure of organic matter. Plants of this family or kind 

 belong to one of the extremes in which the power of absorption is 

 the greatest. But wheat is entirely destitute of this power, and 

 if sown where it cannot obtain its nitrogen from the soil by its 

 roots, it produces no seed, and the quantity found in the plant is 

 less than that which the seed originally contained. From this 

 fact, we see the adaptation of the trefoil to the cultivation of 

 wheat, from the ability which it has of obtaining a supply of 

 nitrogenous matter, where wheat could not in consequence of its 

 peculiar organization. We are particular in stating this fact 

 here, because we have too frequently heard it asserted that wheat 

 derived 97 parts of its substance from the atmosphere, whereas it 

 does not derive any part of it directly from this source, but all 

 from the soil. It is hardly necessary to say, that it is a subject of 

 great practical importance, and it is essential that correct views 

 are disseminated among agriculturists. It is true, however, that a 

 correct practice of farmers has sometimes gone ahead of correct 

 theory, and has sened to sustain them in it, though theory may 

 have been wrong. 



Another interesting point, though it relates to the vegetable 

 physiology, rather than the nature of the process of decay, is w^or- 

 thy of a passing notice in this connection — it is the mode or pro- 

 cess of forming woody fibres, or the relation of starch to lignine. 

 Starch exists in grains made up of concentric layers, or layers 

 one within another, like the coats of an onion. To form starch, 

 it only requires water and carbon; its formula being C. 12, H. 

 10, 0. 10. Now, in a living tissue, carbon being absorbed and 

 carried into it, an equal volume of oxygen is given off or exhal- 

 ed;* the carbon is assimilated by the vital power of the plant, 



•K.ane's Elements of Chemistry, by Draper, p. 652. 



