CAUSES OF ACTION SHOULD BE ASCERTAINED. i!y 



Now all such actions depend on a definite cause, by ascertain' 

 ing which, we place the actions themselves at our command. 



It must be admitted as a principle of agriculture, that those 

 substances which have been removed from a soil must be com- 

 pletely restored to it ; but whether this restoration be effected bv 

 means of excrements, ashes, or bones, is in a great measure a 

 matter of indifference. A time will come, when plants growing 

 upon a field will be supplied with their appropriate manures pre 

 pared in chemical manufactories — when a plant will receive only 

 such substances as actually serve it for food, just as at presen r a 

 few grains of quinine are given to a patient afflicted with fever, 

 instead of the ounce of wood which he was formerly compelled 

 to swallow in addition. 



There are some plants which require humus (as a sou me of 

 carbonic acid), without re-producing it in any appreciable quantity ; 

 whilst others can do without it altogether, and actually enrich a 

 soil deficient in it. Hence a rational system of agriculture would 

 employ all the humus at command for the supply of the former 

 and not expend any of it for the latter; but would in fact make 

 use of them for supplying the others with humus. 



We may furnish a plant with carbonic acid, and with all the 

 materials which it may require ; we may supply it with humus 

 in the most abundant quantity ; but it will not attain complete 

 development, unless nitrogen is also afforded to it ; a herb will 

 be formed, but no grain ; even sugar and starch may be produced, 

 but no gluten. 



But, on the other hand, the supply of nitrogen, in the form of 

 ammonia, will not suffice for the purposes of agriculture. Al 

 though ammonia is of the utmost importance for the vigorous 

 growth of plants, it is not in itseii' sufficient for the production of 

 vegetable casein, fibrin, or albumen. These substances are not 

 known in a free state ; for they are always accompanied by alka- 

 lies, sulphates, and phosphates. We must therefore assume, that 

 without their co-operation, ammonia could not exercise the slight- 

 est influence on the growth and formation of the seeds ; that, in 

 such a case, it is a matter of perfect indifference whether anrt- 

 monia is conveyed to them or not ; for it will not assist in th8 

 formation of the constituents of the blood, unless the other condi* 



