72 BOARD OF AQRICULTURE. 



ration, gaining a very accurate knowledge of the structure of 

 plants ; second, that of chemical experiment, by which the con- 

 stituent elements of plants, their means of sustenance, and some 

 tran^foi'malions of their substance occurring during growth, have 

 been ascertained. 



" From the results arrived at by these researches, a special sci- 

 ence, called Vegetable Physiology, or the knowledge of the vital 

 phenomena, conditions and laws of plants, has been attained, and of 

 this scioncc Agricullural Chemistry constitutes apvinclpal division."* 



Among the problems connected with practical agriculture which 

 this science has to solve, that relating to the nourishment of plants 

 is most important. For if the farmer knew what nutrients would 

 best promote the growth of his plants, in what form, quantity, and 

 at what period they must be applied, to best results, — if he were 

 acquainted with the sources of their cheapest supply, "he would 

 be able to make the most extensive, diversified, and profitable ap- 

 plication of this information in his calling." But science is not 

 matured to furnish all this with certainty. 



In the case of animals, by our senses we are able to perceive 

 what they take as food, and how they take it ; not so with plants. 

 We know that soil, moisture, air, warmth and light, are necessary 

 to the growth of plants, but as the soil, the w^ater, and the air 

 contain very dissimilar elements, the essential point is to find 

 which of these separate elements are received by the plants as 

 nourishment. Here arises a necessity for an exact knowledge of 

 the chemical elements of the plant itself, as well as of the soil, of 

 water, and of the air. 



The first question then is, of what do plants consist ? As the 

 main pillar of their structure, as well as that of all living creatures 

 upon the earth, four elements particularly claim our notice. They 

 are called, oxygen, hydrogen, carbon and nitrogen. These receive 

 a general name of organic constituents ; also called combustible ele- 

 mentary substances ; and sometimes take the name of atmospheric 

 elementary substances, because they are contained in atmospheric 

 air. But I do not propose to be led so far from the direct line of 

 my subject as to attempt to show our daily dependence on the 

 whole vegetable kingdom ; but I'ather to speak of that class of 

 plants called trees ; and these are more nearly composed of the 

 three elements, carbon, hj^drogen, and oxj'-gen, which three simple 

 elements make up about 90 per cent, of their structure. 



*Dr. J. A. Stoeokhardt. 



