XU CONTENTS. 



Sect. 2. Definitions and descriptions . — Source and assimilation 

 of the organic constituents of jtlants. 



Definition and description — ]. Of huniin , . . . 135 



2. Of humic acid. 3. Of crenic acid. 4. Of apocrenic acid 136 



5. Of apocrenates. 6. Extract of humus .... 137 



Source of organic constituents. 



I. Carbon. History. Nature of vegetable mould . , 138 



Theories 



I. Of Liehig. Arguments in support of Liebig's theory , 140 



1. Quantity of carbon introduced in the form of humate of lime 141 



2. '< " by metallic oxides . . 141 



3. " " by water .... 141 



4. Quantity of carbon yielded by wood land, meadows and 



ploughed fields 142 



Origin of the carbon of the first vegetables .... 142 



Quantity in the atmosphere invariable. Why ? . . . 143 



How is the carbonic acid of the atmosphere disposed of.? . 143 



5. The most important function in the life of plants— what ? 144 



6. Nature of decay— changes which take place . . . 144 



7. Excrementitious matters of the roots 145 



Objections to Liebig's theory. 



1. This theory does not give acorrect view of the humus of soil 146 



2. The facts which are brought forward do not prove it, 



allowing them their full force 146 



3. This theory does not give a correct view of the quantity 



of water in the soil 147 



4. This theory overlooks the influence of living plants . 147 



5. There are evidently other sources of carbon . . .148 



6. The theory is inconsistent with itself and with facts . 148 



7. " " must therefore be modified . . . .149 

 Other sources of carbon, humic, crenic and apocrenic acids , 150 

 Summary of the sources of carbon 151 



TIteory of the assimilation of carbon 

 Illustrated by chemical transformations . . . .151 



Chemical transformations in plants and animals . . . 153 



II. Source of the hydrogen of plants. 



1. Water. 2. Ammonia. 3. Light carbureted hydrogen . 155 



4. Geine or humus 155 



ni. Sources of the oxygen of plants. 



1. The atmosphere. 2. Water 155 



3. Carbonic acid. 4. Geine or humus. 5. Nitric acid . 156 



