465 



the mode of investigating the composition, and of studying the charac- 

 ters, of the different substances from which plants derive their nourish- 

 ment." — p. 7. 



" Innumerable are the aids afforded to the means of life, to manufac- 

 tures and to commerce, by the truths which assiduous and active in- 

 quirers have discovered and rendered capable of practical application. 

 But it is not the mere 'practical utility of these truths, which is of im- 

 portance. Their influence upon mental culture is most beneficial ; and 

 the new views acquired by the knowledge of them enable the mind to 

 recognise in the phenomena of nature proofs of an infinite wisdom, for 

 the unfathomable profundity of which human language has no expres- 

 sion." — p. 6. 



The work is devoted to an explanation of the proper food of plants, 

 and the modes in which, and sources from which, they receive this 

 nourishment. Connected with these matters, come, of course, the value 

 and uses of manures, and the true art of culture. These subjects are 

 all obviously of the highest importance ; and it is exceedingly interest- 

 ing to see how a mind so powerful and learned discusses them. The 

 author speaks with just respect of that distinguished man, the late Sir 

 Humphrey Davy, who first taught systematically the application of 

 chemical science to agriculture ; and he shows himself not an unworthy 

 pupil of so eminent a master. We can do but imperfect justice by an 

 abstract of his views ; yet it is all for which we have room. 



The elements or constituents of all plants are carbon, water, (or its 

 elements, hydrogen and oxygen,) nitrogen, and some earthy or alkaline 

 salts. The food of plants can be received only in a gaseous or soluble 

 form, and it must come from the atmosphere, from the earth, or from 

 both. No earthy substance can ever be received into a plant unless 

 in a dissolved or combined state ; and though crude substances, inca- 

 pable of assimilation, may in som.e cases be taken up by the roots of 

 the plant, which seem to have no power of selection in regard to their 

 food, yet they will be exuded from the roots in the state in which they 

 were received. The alkaline substances received and assimilated by 

 plants can only be ascertained by their ashes after incineration, and 

 constitute a very minute portion ; but, however minute, they are evi- 

 dently essential to the perfection or fructification of the plant. Besides 

 these there are certain organic acids, which are found in the juices of 

 plants and usually combined with some inorganic bases. The alkaline 

 bases or earths must exist in the soil, or they cannot be found in the 



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