168 REPORT — 1861. 



The preceding experiruents, I think, furnish convincing proofs that, through 

 the instrumentality of purely nitrogenous manures, the produce of our grain- 

 crops may be very considerably increased, whilst the same manures appear to 

 be of no beneficial effect upon root-crops, at least on soils similar in character 

 to those on which the experiments were made. 



In making this statement, it is not maintained that mineral matters are less 

 essential to cereals than to root-crops ; for I take it for granted thai no che- 

 mist or vegetable physiologist at the present time will consider the ash- 

 constituents of plants less essential for cereals than for turnips and other 

 root-crops. No amount of nitrogenous manure can replace these earthy 

 matters, which enter into the composition of all cultivated plants. 



But, at the same time, it is a matter of experience that on many soils no 

 reasonable amount of mineral fertilizing constituents will increase the yield 

 of wheat or barley, whilst on these soils a moderate amount of a purely 

 nitrogenous manure will contribute to a large increase in the amount of 

 corn which can be raised from the same soils. 



It is hardly necessary to say, that the larger increase, as a matter of course, 

 removes more mineral matter from a land dressed with an ammoniacal or purely 

 nitrogenous manure than from land not so treated ; nor can it be denied 

 that on sandy and naturally sterile soils the application of fertilizing materials 

 containingexclusivelynitrogen, in some form or theother.will tend to the rapid 

 exhaustion of such soils ; it is nevertheless a fact that the great majority of 

 English soils are so rich in mineral matters that no fear need be entertained 

 of the land becoming permanently deteriorated by the occasional use of 

 nitrogenous matters on wheat-soils. 



With respect to the combination in which nitrogen appears to be most 

 generally assimilated by plants, and to be most grateful to wheat and barley, 

 and probably to vegetation in general, I am of opinion that nitric acid is 

 by far the most usual form in which nitrogen is taken up by plants. Nitrates 

 certainly produce a more rapid and more energetic effect than ammoniacal 

 salts on all plants which are benefited by nitrogenous matters. 



Nitrates have been found, by Dr. Sullivan and by myself, in a great variety 

 of plants, and may be detected without much difficulty in everj' arable soil, 

 when a suflBciently large quantity of soil is operated upon. In porous lime- 

 stones, and in soils containing chalk and gravel, ammoniacal salts appear to 

 be readily transformed into nitrates; hence the constant presence of traces 

 of nitric acid in the limestones of buildings, and of the occurrence of nitrates 

 in more considerable quantities in the well-water of towns. During the 

 period of the most energetic growth of plants, that is, during the summer 

 season, the process of nitrification no doubt proceeds with greater rapidity 

 in the soil than during autumn and winter ; and, in all probability, the luxu? 

 riant growth of plants during summer is materially assisted by the greater 

 proportion. of nitrates in the soil. Ammoniacal salts certainly benefit vege- 

 tation, and so do nitrogenous organic matters, but it may be questioned 

 whether these matters have not to be ultimately converted into nitrates 

 before they can be of real utility to vegetation. Taking into account all the 

 laborious experiments which have been made of late by Boussingault, by 

 De Ville, and Dr. Gilbert and Mr. Lawes, with respect to the assimilation 

 of nitrogen by plants, and bearing in mind agricultural experience and the 

 results of direct manuring experiments, I think we shall find — 



1. That there is suflficient evidence for regarding the free nitrogen of the 

 atmosphere as incapable of supplying plants with food M'hich they can utilize 

 in forming albuminous matters. 



2. That nitrogenous organic matters, such as hoofs, horn, wool, hair, and 



