BULLETIN OF THE BUSSEY INSTITUTION. 285 
its physical peculiarities ; but the discussion of these points would be 
altogether foreign to the present inquiry. Their importance has indeed 
often been insisted upon. It is to be remarked, moreover, that the 
experiments and observations here presented do not in any way con- 
flict with the exceedingly important conclusions that have been reached 
of late years, concerning the formation of active nitrogen compounds 
from the free nitrogen of the air * by the action of ozone, and in vari- 
ous processes of combustion and oxidation. The importance of such 
sources. of nitrogen for the growth of plants in earlier geological epochs, 
and for the support of lichens, mosses, and other inferior forms of 
vegetation in our own times, can hardly be over-estimated. It is 
to be supposed, indeed, that the influence of these supplies of nitrogen, 
though exceedingly feeble, must be very widely felt. To them, undoubt- 
edly, in the last analysis, the existing stock of soil-nitrogen is to be 
chiefly attributed. ‘The fixation of the free nitrogen of the air by soils 
rich in organic matter, that has been noticed repeatedly by Boussin- 
gault,t and by other observers, and strongly insisted upon of late by 
Dehérain ¢ is another fact, perhaps of the same order, to be kept in 
mind. But there can be little doubt that, for the present support of 
agricultural crops, the vast stores of vegetable mould that have accu- 
mulated in the soil through the decay of many generations of plants, 
constitute a more abundant and a more important source of nitrogenized 
plant-food than any other. 
* See Johnson’s ‘‘ How Crops Feed,’”’ New York, 1870, pp. 75-85. 
t See, for example, his “ Agronomie,” 1. pp. 8038, 808, 821, 828 § 5, 836, 
and 844. 
t In his “ Cours de Chimie Agricole, Paris, 1878, p. 316, and in papers in the 
“ Comptes Rendus” of the French Academy. 
