ELEMENTS OF PLANTS. 243 



Patting aside for the present the minute proportion of inorganic 

 elements (or ashes) of plants or supposing their amount to bo 

 always ascertained separately, or understood the great remainder 

 of all plants, amounting from more than nine-tenths of the dry 

 weight of some products to more than ninety-nine-hundredths of 

 others, consists of elements which also constitute air and water, or 

 are always present in the atmosphere ; and which therefore are 

 always surrounding all growing plants, and in unlimited quantities. 

 But though so abundant and inexhaustible, these elements cannot 

 be taken up by growing plants except under certain conditions j 

 and these conditions are but slightly under the control of cultiva- 

 tors, or even known to the present researches of science. 



Of the four great elements of organic bodies, carbon only is 

 ever presented to our senses, alone and as a solid. Charcoal is 

 nearly pure carbon; and the brilliant and precious diamond "is pure 

 crystallized carbon. Of the three other great elements, oxygen, 

 hydrogen, and azote, each one in its separate state is only known 

 to us as gas, or air; and however different and potent their quali- 

 ties, they are all as little perceptible by our sight or touch, as the 

 atmosphere. Further: carbon, though existing nearly pure, and 

 visible and tangible, as. charcoal, yet, when in that state, is incapa- 

 ble of affording any direct support to plants ; for which office it is 

 necessary that carbon shall be combined with oxygen ; which com- 

 bination also forms a gas (carbonic acid), in which state it is dif- 

 fused throughout the atmosphere, and in which only it is fit to be 

 received into plants, through their leaves, and thus to furnish to 

 them their essential element, carbon. 



Thus, the materials of nearly the whole solid substance of all 

 plants and all animal bodies, are supplied wholly by four gases, or 

 different kinds of air. This proposition (than which none in agri- 

 cultural chemistry is better established), when first heard, may 

 well seem too mysterious for comprehension, and the results too 

 wonderful for belief. And after -the proposition has been fully 

 assented to, there must occur to the mind of every student of this 

 interesting subject another question involving as much of mystery 

 and wonder, if not also of doubt. This question is, "If the 

 atmosphere always contains all the organic constituents of plants 

 in inexhaustible quantities and if plants derive from the atmos- 

 phere nearly all of their constituent parts why should they ever 

 suffer for want of a sufficient supply of nourishment, whether 

 growing on rich or poor soils ?" The answer is, that the laws of 

 nature forbid some of these gaseous bodies to be taken up directly 

 by growing plants or, at least, only under certain conditions ; 

 and these conditions are not dependent on the quantities of these 

 gases present in the surrounding atmosphere, and are but slightly 

 under the control of man ; limited in knowledge as at present. 



