328 HOW CROPS GEOW. 



cells ; they also imbibe such salts as the water of the soil 

 holds in solution; they likewise act directly on the soil, 

 and dissolve substances, which are thus first made of avail 

 to them. The compounds that the plant must derive from 

 the soil are those which are found in its ash, since these 

 are not volatile, and cannot, therefore, exist in the atmos- 

 phere. The root, however, commonly takes up some other 

 elements of its nutrition to which it has immediate access. 

 Leaving out of view, for the present, those matters which, 

 though found in the plant, appear to be unessential to its 

 growth, viz., silica, soda and manganese, the roots absorb 

 the following substances, viz. : 



Sulphates "] f Potash. 



Phosphates [ J Lime. 



Nitrtites and | '. Magnesia and 



Chlorides J [ Iron. 



These salts enter the plant by the absorbent surfaces of 

 the younger rootlets, and pass upwards through the active 

 portions of the stem, to the leaves and to the new-forming 

 buds. 



The Leaves, which are unfolded to the air, gather from 

 it Carbonic A.cid Gas. This compound suffers decompo- 

 sition in the plant ; its Carbon remains there, its Oxygen 

 or an equivalent quantity, very nearly, is thrown off into 

 the air again. 



The decomposition of carbonic acid takes place only by 

 day and under the influence of the sun's light. 



From the carbon thus acquired and the elements of wa- 

 ter with the cooperation of the ash-ingredients, the plant 

 organizes the Carbohydrates. Probably glucose, perhaps 

 dextrin or soluble starch, are the first products of this 

 synthesis. 



The formation of carbohydrates appears to proceed in 

 the chlorophyll-cells of the leaf 



The Albuminoids require for their production the pres- 

 ence of a compound of Nitrogen. The salts of Nitrio 



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