HOKTICrLTUBAL «OCIETT OF LOXDOX. 



S27 



start from, have laid the foundatioD of a complete and practical 

 system of .\^cultural Chemistry. The great sources of the food 

 of plants have been traced oat, and determined : the manner ia 

 which they obtain the various elements necessary to their growth 

 has been investigated, and attention has been drawn to the im- 

 portance of studying the nature of the inorganic substances 

 always present in plants in small quantities. Liebig has more 

 especially drawn attention to the necessity of supplving these sub- 

 stances to growing plants, as well as of those which more pro- 

 perly speaking constitute their food, namely such as supply them 

 with carbon, oxygen, hydroffen, and nitrogen, the four elements, 

 which by entering into combination with each other in different 

 proportions give rise to the formation of woody fibre, gum, starch, 

 gluten, and all the various proximate elements of plants, and 

 which consequently compose the whole of their organic struc- 

 ture. It has long been known that independent of the action of 

 heat, light, and moisture, it is essential to the growth of plants 

 that they be supplied with oxygen, hydrogen, nitrogen, and 

 carbon, the elements of which they are composed, but Chemists 

 and Physiologists have differed greatly as to the manner in which 

 plants obtain these elements, and consequently as to the use and 

 more of action, both of soil and manure. The recent writings 

 of Liebig have done much towards explaining these processes, for 

 not being a physiologist and therefore having no peculiar physi- 

 ological views to support, he has argued on known facts merely 

 as a chemist, and explained in a clear and scientific manner the 

 chemical processes of vegetation, which were previously either 

 not understood at all, or but imperfectly and in many cases erro- 

 neously accounted for. 



Much has been written on the source of Cabbox, and the state 

 which it must be in to enable it to enter into the organs of plants 

 and assist in their srowth by undergoing assimilation. It was 

 long ago believed by Drs. Ptiesiley and Ingenhousz as well as 

 other observers, that plants derive the carbon which they contain 

 from the carbonic acid always present in the air. They observed 

 that it was impossible for the carbon contained in a large tree for 

 example, to have been possibly derived from the soil, because 

 the space of eanh through which the roots of such a tree spread 

 never contains carbon enough to supply the very large quantity of 

 that elemoit required by the tree. They therefore conceived that 

 the carbon was derived from carbonic acid, partly from that existing 

 in the air and partly from gas generated in the soil by the gra- 

 dual oxidation of carbonaceous matters. More recently a theory 

 was staned which derived considerable importance from the 

 names of the eminent chemists who supported it : it was supposed 



