THE CONSTITUENTS OF PLANTS. 11 



The Essential Constituents, How Determined. 

 The sources of the chemical constituents necessary to the 

 growth of plants, as well as their kind and number, 

 have been determined by careful experiments, conducted 

 in the following manner : 



Sand, which is an inert substance, is thoroughly burned, 

 which destroys all combustible matter; then carefully 

 washed, which removes all traces of plant-food ; a por- 

 tion is then put in a suitable jar or box, and seed of 

 wheat or corn planted, and moistened with pure distilled 

 water. The sand contains no food, yet the weight of 

 the dry matter in the growth made is shown, by careful 

 analysis of both seed and plant, to be much greater than 

 the weight of the seed planted; also, that the increase 

 in weight consists entirely of carbon, hydrogen, and 

 oxygen, which must have been obtained from the air 

 and water. This establishes the fact that air and water 

 furnish food, and that this food consists of atmospheric 

 elements. 



In another series of experiments, to the sand and water, 

 in one experiment, the various essential ash or mineral 

 constituents alone, are added; to another, nitrogen alone; 

 while to a third, both the ash constituents and nitrogen 

 are added. In the first and second experiments, but little 

 addition is made in the weight of the crop over that 

 secured when water alone was added ; the growths are not 

 perfect; minerals alone, and nitrogen alone, are not suffi- 

 cient. In the third experiment, however, the crop is fully 

 developed in every particular, proving that the addition 

 of minerals and nitrogen is absolutely essential. 



The necessity of each of the mineral constituents, and 



