LAW OF PLANT-LIFE. 143 



could be applied in practical agriculture. The statement of 

 principles has been, that scientific men know absolutely what 

 plants are made of; that the composition of perfectly mature, 

 healthy, well-developed plants is unvarying. The composi- 

 tion of plants is not an accident, but a design. The wheat 

 plant of to-day, in its composition, in obedience to natural 

 law, is practically the same thing that it was a thousand years 

 ago, and is in its composition to-day practically what it will 

 be a thousand years hence. Law, and not accident, controls 

 it ; and that is true in relation to all the plants of our fields. 

 The statement has been made, that, in relation to the materials 

 of which plants are composed, all, so far as the plants are 

 concerned, are equally important. If a plant takes a frac- 

 tion of one per cent, into its composition of soda, for exam- 

 ple, that one fraction of one per cent, of soda is just as im- 

 portant to the plant as ten or fifteen per cent, of lime or of 

 potash ; and so with every other element that enters into its 

 composition. To the plant, all the elements that enter into 

 its composition are absolutely essential, or a perfect plant 

 cannot be formed. It has been stated, that, so far as the 

 farmer is concerned, — the man whose business it is to feed and 

 to produce plants, — there is a wide difference in the importance 

 of the different elements which enter into the composition of 

 plants ; as, for instance, while every plant which is formed 

 must have a large per cent, in its composition of carbon, and 

 it cannot be formed without carbon, yet, so far as the farmer 

 is concerned, he may throw this part of the plant's composi- 

 tion entirely out of his account, and he need never feed a 

 plant with carbon. It has an exhaustless supply of this from 

 natural sources. So with the other orgauic elements of plant- 

 nutrition, with the exception of nitrogen. Nitrogen, which a 

 large proportion of our plants take in large quantity, the 

 plant cannot get its full supply of from natural sources, 

 although it may draw much ; and nitrogen the farmer must 

 supply. So with the other elements. While the plant must 

 have soda in its composition, yet, so far as the farmer is con- 

 cerned, soda can be supplied by the soil itself in sufficient 

 quantity for. all the plants that will probably be produced 

 upon it, and the farmer need never supply soda for the food 

 of plants. The standard of the maximum yield of crops on 



