88 ANATOMY AND PHYSIOLOGY OF 



rience that ammoniacal salts mixed witli the soil, greatly further 

 the growth of plants. These diffeient results render it in the 

 highest degree probable tliat tlie ammoniacal salts enter into com- 

 binations ^-vith the constituents of the soil, which exercibe a dif- 

 ferent action upon the plants, from that of the pure salts. In this 

 respect the investigations of Mulder upon the humous substances 

 are of the highest value. Accoiding to these, carbonate of ammonia 

 cannot exist for any time as such in humous, but is decomposed by 

 the organic acids of the soil; since therefore compoiinds of ammonia 

 with sulphuric and hydrochloric acids, fee, must be converted by 

 the carbonate of lime in the soil into carbonate of ammonia, there 

 exists the highest probability^', that plants always receive ammonia 

 in combination with the organic acids of the soil, which would 

 explain the difference between the poisonous action of pure ammo- 

 niacal salts and their favourable influence when mingled with the 

 soil. Moreover, it is not by any means proved that the air con- 

 tains enough ammonia for us to regard it as anything like a suffi- 

 cient source of nitrogen to plants, while Muldei's experiments 

 point to a production of it in the soil ; in any case the amount 

 contained in the soil is very considerable, according to Kidcker 

 (Bei'zelius, " JaliresheTicht," xxvi. 265) it amounts to 4045 

 pounds in a layer ten inches deep extending over a hectare in 

 sandy soil, 2 OS 1 4 in argillaceous soil. From these ciicumstances 

 as well as from the expermients of Boussingault and Mulder, it in 

 any case follows, that the roots and not the leaves take up the 

 substances which furnish plants with nitrogen, while, on the con- 

 trary, the leaves play the especially active part in the absorption 

 of carbonic acid. 



d. Elaboration of the Nutriment, 



"We know scarcely anything of the chemical processes in the 

 interior of plants, on which depend the assimilation of the nutrient 

 matter taken up, and the gradual conversion of this into the 

 various compounds which the plant contains. In considering the 

 nutritive processes of plants, two circumstances first strike us. 

 1, The uncommonly great agreement of all plants in lespect to the 

 prifduction of a series of neutral hydrates of carbon, which furnish 

 the material for the solid parts of plants, as also in respect to the 

 formation of proteine-substanees which play an active part in the 

 process of development of the cell ; 2, ^n infinite variety of chemi- 

 cal compounds, which are deposited in the different organs of 

 particular groups of plants, in spite of the uniform structure 

 and the agreement in the nutrient process, so far as relates to 

 growth. 



The chemists of our days, especially Mulder, have sought to 

 make comprehensible the formation of such a surprising abundance 

 of products by bodies so simply and uniformly organized as plants 



