58 SCIENTIFIC AGRICULTURE. 



forces which tend to produce decomposition, or transformation 

 of their elements. Substances of different properties, but 

 identical in composition, are called isomeric bodies. 



These bodies, although containing the same ultimate ele- 

 ments, may be as widely different in their chemical relations 

 as bodies which have no elements in common. Oil of turpen- 

 tine and oil of citron are isomeric compounds, each being 

 composed of carbon 5 hydrogen 4. 



LIGNINE. 



The proper wood of plants, when separated by chemical 

 means from all soluble substances, is called lignine. It is 

 composed of carbon, hydrogen and oxygen, these are its 

 constant elements, whether it be obtained from the porous 

 willow, dense boxwood, or the fibres of linen and cotton. The 

 hydrogen and oxygen exist in the same proportions as in 

 water; so that lignine is apparently only carbon and water: 

 but distillation does not prove this to be the case. 



Pure lignine is white: it undergoes no decomposition in dry 

 air, or under water which contains no air; but by the joint 

 action of heat and air it undergoes changes which produce 

 another series of compounds, very different from itself. Woody 

 fibre is arranged in cells and tubes : the walls of these cells 

 and tubes are composed of cellular woody fibre, and covered 

 by a solid substance called incrusting matter. It is difficult to 

 separate the two, so as to determine by analysis the precise 

 difference in their composition. It is evident that woody fibre 

 constitutes the great mass of all forest trees, and also of the 

 dried stalks and roots of most plants. 



STARCH. 



Starch is probably the most abundant product of vegeta- 

 tion, with the exception of woody fibre. It is obtained from 

 the flower of all the grains, many roots, the .pith and seeds of 

 many other plants. Starch is obtained in the form of a fine 



