Proceedixgs of the Farmers' Club. 851 



may be the most conveniently considered under the two heads of 

 those which, for the most part, yield ammonia, and those of iron, silica, 

 phosphoric acid, snlphuric acid, chlorine, and more rarely manga- 

 nese, iodine and fluorine. All of these are generally found in the 

 soil in sufficient quantities, except potash and phosphoric acid. In 

 addition to these the soil must have ammonia, which is most fre- 

 quently deficient, so that, as a general rule, effectual manuring means 

 sim])ly this, the plentiful supplj* of potash, phosphoric acid and ammo- 

 nia to the soil ; and any specimen of the class of fertilizers of which 

 we are now speaking is valuable just in the proportion in which it 

 contains these substances in a soluble forna. We say in a soluble 

 form ; for each and every one of the constituents we have mentioned 

 must enter the roots of the plants dissolved iu water, and that, too, 

 in sucli a minute state of subdivision that for every grain of mineral 

 matter deposited in which, owe their value chiefly to the phosphoric 

 acid contained in them; but it must be borne in mind that it is very 

 difficult to draw the exact line between these two last mentioned varie- 

 ties of manures, inasmuch as many of those which contain the 

 largest amount of ammonia possess also a considerable percent- 

 age of phosphoric acid. There are about a dozen mineral sub- 

 stances which enter into the composition of vegetables, and 

 which, in some form or other, must exist in the soil to mahe it 

 productive for all kinds of plants. Tliese are potash, soda, lime, 

 magnesia, peroxyd of iron, silicic acid, phosphoric acid, sulphuric 

 acid, chlorine, and, in less numerous instances, iodone, fluorine and 

 manganese. These all enter the root spongioles in solution in water, 

 and so dilute is this solution, that in order to enable the aggregate 

 of the mineral constituents of a plant to enter its organism, not 

 less than two thousand times its weight of water must pass 

 into the plant and be exhaled from its leaves ; and hence we see 

 that it is not enough in estimating the value of a fertilizer to 

 know merely the quantity of enriching material that it contains, 

 but we must be aware as well of the comparative facility with 

 which these materials may be dissolved, and thus brought into 

 proper condition to be absorbed by the roots. It should be men- 

 tioned in this connection that although more than one-half of the 

 substance of all vegetable organizations consists of carbon, which in 

 the form of carbonic acid enters the plant for the most part through 

 the leaves, the .carbonic acid generated from manure applied to the 

 soil acts only a; secondary part in improving the land itself, which it 



