ARTIFICIAL MANURING. 139 



If the nitrog'en and carbonic acid formed by tlie decay 

 and decomposition of the vegetable ing-redients of manure 

 were the cause of its fertilizing- power, this oug"ht also to be 

 seen if the mineral substances are excluded. Direct experi- 

 ments liave shown that the nitrog-en of the excrements can 

 be assimilated by the plants in the form of ammonia ; but 

 that ammonia, as well as carbonic acid, althoug-h it is indis- 

 pensable for the development of all plants, can accelerate the 

 growth of plants and increase the produce of a field of grain, 

 roots, and tubercles, only if at the same time the mineral in- 

 gredients contained in the manure which is applied are in a 

 state in which they are suited for assimilation. If the latter 

 are excluded, carbonic acid and ammonia have no effect on 

 vegetation. 



On the other hand, ex])erience has shown that on many 

 fields the produce which is rich in carbon and ammonia can 

 be increased to an extraordinary amount without any supply 

 of such matters as furnish these substances. 



On fields which are provided with a certain cpiantity of 

 marl or slacked lime, or with bone-earth and gypsum — sub- 

 stances which cannot give up to the plants either carbon or 

 nitrogen — rich crops are obtained, in many places, of grain, 

 tubers, and roots, entirely in contradiction with the view 

 which ascribes the eflfect of the manure to its amount of in- 

 gredients containing nitrogen or carbonic acid. 



To ex})lain this process, which is so opposite to the com- 

 mon opinion, the marl, the lime, the gypsum, the alkalies, 

 and the bone earth were regarded as stimulants, which acted 

 on the plants like spices on the food of man, of which it was 

 believed that they increased the power of assimilation, and 

 allowed the individuals to consume larger cpumtities of food. 



This view is contradicted if we consider that stimulants 

 mean such substances as do not serve for the nourishment of 

 the organism or for the formation of org-anic elements, and 

 can only increase the weight of the body if at the same 

 time a certain increase of food is given. In supplying the 

 fields with the above mentioned substances the weight of 

 the plants becaiue increased in all their separate parts, w^ith- 

 out their having been provided wath the quantity of food 

 which, according to theor}^, was necessary to this extraordi- 

 nary increase, viz., with carbonic acid and ammonia. 



Chemical analysis shows that these so called stimulants 

 are either actual ingredients of manure, as gypsum, bone 

 earth, and the active substances of the marl, or that they 



