270 BULLETIN OF THE BUSSEY INSTITUTION. 
of the apparent anomaly is not far to seek. The country around 
Nantes and Rennes, and throughout the districts where bone-black is 
so largely used, is a region of granitic rocks rich in potash,* and the 
clayey or gravelly'soils (sols argilosiliceux) that have resulted from the 
- disintegration of these rocks, are naturally abundantly provided with 
one of the important elements of the food of plants; namely, potash. 
There is consequently little or no need of applying a “ general” or “ com- 
plete” manure to these soils. But it is plain, on the other hand, that the 
phosphatic element of plant-food is lacking in these soils, since long 
experience has shown that phosphate of lime applied to them in the 
form of bone-black serves an excellent purpose. The use of potash as 
‘amanure in that region seems to be well-nigh or even quite unnecessary ; 
and it is clear, moreover, as it concerns us particularly to note in this 
connection, that the nitrogen naturally contained in the soil must play 
a very important part in supporting the crops that are obtained, since 
in actual farm practice the special phosphatic manure is used either 
with or without addition of nitrogeneous manure, accordingly as the 
soil of the field to which it is applied contains a small or a large pro- 
portion of vegetable remains. In other words, the bone-blacks that 
contain no nitrogen are used upon new land, as has been said, while 
those charged with blood and other albuminous matters are applied by 
preference to “soils that have been exhausted by a long course of cul- 
tivation ” (Bobierre, op. cit., p. 279.) 
The use of wood-ashes by themselves here in New England and 
elsewhere, upon soils that are naturally poor in potash, is another in- 
stance of the same general character. It would be easy to cite a great 
number of experiments in which crops manured with ashes have mani- 
festly made use of the nitrogen in the soil. The fact is particularly 
well illustrated in some of my own experiments upon the growth of 
barley, beans, and ruta-bagas upon a soil not specially rich in vegetable 
matters (see pages 89, 106, 136, and 140) ; since in these experiments not 
only wood-ashes but simple potash salts, such as the sulphate and the car- 
bonate, applied in the pure state gave exccllent ‘results. It has been 
shown by Boussingault that traces of cyanides and of other compounds 
of nitrogen are sometimes retained in the ashes of plants; but the 
* Bobierre, op. cit. (page 106), gives the analysis of a gneiss from this 
region that contains nearly 8% of potash. 
tT In his “ Agronomie,” 1. pp. 86-93. 
