BULLETIN OF THE BUSSEY INSTITUTION. a fi} 
of cultivated crops. In almost any locality instances may be seen of 
forest-trees and other wild plants so situated that their nitrogenous 
food must manifestly be derived, in great part, if not wholly, from this 
source. In the immediate vicinity of Boston, for example, a great 
‘variety of weeds may be seen growing upon mere gravel in places 
where the original levels of the land have been changed to make room 
for the erection of buildings or for the laying out of roads, in such sort 
that the surface-soil has been completely dug away, and the subsoil 
laid bare; and their growth is doubtless to be explained by a reference 
to the nitrates and nitrogenized organic matters that are contained in 
_the soil-water, and brought therewith to the roots of the plants by the 
capillary action of the gravel. It has been shown in a previous paper 
(pages 56-58), that the drift gravel of this vicinity can supply of 
itself the inorganic elements of plant-food, and several observers have 
found that well-waters often contain food enough of all kinds to support 
a tolerably vigorous growth.* 
On the other hand, ammonia is doubtless produced ma the soil- 
nitrogen in some cases,f though it can no longer be deemed to be 
abundant or even important in the sense that Liebig + sometimes 
taught. 
I am myself inclined to attach no little importance to the presence 
in the soil of minute forms of animal and vegetable life, that obtain 
their nitrogenous food directly from the vegetable mould, and yield in 
their turn, both by their excretions and by the decay of their dead 
bodies, a supply of nitrogenous compounds of the kinds that are fit to 
be taken up by plants. ‘This idea is an old one. It was suggested by 
Ehrenberg, $ who maintained long ago not only that microscopic animals 
* Compare Johnson’s “‘ How Crops Grow,” p. 171. For the amounts of 
nitrates that have been found in well and river waters; see Knop’s “‘ Agricultur- 
Chemie,” 2. 60. 
{ Compare Boussingault in his “ Agronomie,” 2. pp. 18, 210; 3. 196, and 
elsewhere ; and Johnson in ‘‘ Peat and its Uses,” p. 45. 
t See, for example, his “Theorie und Praxis in der Landwirthschaft,” 
Braunschweig, 1856, p. 5. 
§ According to Cohn, in Steckhardt’s “ Chemische Ackersmann,” 1863, 9. 
, pp. 221, 222. The idea has a certain resemblance to that of De Saussure 
(“ Recherches,” p. 166), who thought that the carbonate of ammonia which is 
evolved on subjecting vegetable mould to dry distillation must be derived in 
part from “insects that live in the humus and leave their remains there.” 
Compare the observations of Boussingault in his “ Agronomie,” 1. pp. 844, 
