CHEMICAL ELEMENTS OF PLANTS. 169 



wished that once at least in every summer these inestimable 

 blessings might become visible as they rise in beautiful though 

 unseen forms and mingle with our atmosphere. On that 

 occasion surely, thoughtless and ungrateful men would be con- 

 strained to admire the wonderful Avorks of the Creator. 



The chemical elements of plants and animals are of course 

 identical. Three are very common in all organic tissues, — 

 carbon, oxygen and hydrogen, — and three more are found 

 wherever there is life, though usually in very small quantity, 

 — nitrogen, phosphorus and sulphur. Besides these there are 

 a few metals which are essential to the growth of healthy and 

 perfect plants. Thus iron in very minute proportion is found 

 in the green coloring matter, or chlorophyl of every plant, 

 and chlorophyl may be regarded as analogous to the gastric 

 juice of animals, since without it plants are incapable of 

 digesting carbonic acid, or elaborating cambium, or other 

 organizable matter. Potassa, lime and magnesia are also 

 necessar}' ingredients in the food of all plants, and though 

 they are scarcely to be regarded as constituent parts of any 

 vegetable tissue or product, they are absorbed by the roots, 

 circulate in the sap, and are probably deposited in all cells, 

 since a greater or less quantity of incombustible ash remains 

 whenever they are burned. Their presence doubtless aids in 

 the formation of vegetable acids and other compounds, and 

 assists in the transference of elaborated or assimilable 

 materials from one part of the plant to another. A few 

 other elements are taken up in variable quantities by living 

 roots, but can hardly be considered as deserving of attention 

 at this time. 



It is a fact worthy of special notice that the amount and 

 kind of mineral matters absorbed by a growing plant may .be 

 caused to vary greatly l3y artificial treatment, and Professor 

 Goessmann has shown, in his report on the sugar-beet, for 

 1871, that this plant exhibits remarkable changes in its ash- 

 constituents, as well as in its percentage of sugar, as the 

 result of cultivation. The ash of the wild beet contains more 

 soda than potassa, but the best and sweetest sugar-beets now 

 contain at least three times as much potassa as soda. As a 

 soda plant therefore it was worthless, having scarcely a trace 

 of sugar, but the physiological chc^nges produced by artificial 



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