14 BULLETIN OF THE BUSSEY INSTITUTION. 
cial manures. As has been stated already on page 269 of the first 
volume of this Bulletin, the fertilizing effects produced by spent bone- 
blacks upon the soils of south-western France indicate as clearly as 
the analyses of the rocks of the region that potash must there be natu- 
rally abundant in the soil. It is a question whether the good effects 
obtained by the use‘of nitrogenized superphosphates in many special 
localities in this country might not be explained in like manner by 
the intelligent observation of the rocks of these localities and of the 
influence which the products of their disintegration exert upon vege- 
tation. 
The fertilizing influence of the wash of roads in some localities 
and of street-sweepings has been often remarked, and the traditions 
concerning them are sufficiently familiar to most practical men. But, 
as Steeckhardt* long since pointed out, what little value these sub- 
stances may really possess must largely depend upon the composition 
of the stones or gravel of which the road has been built. The fertil- 
izing action of the wash or the sweepings is doubtless due, in most 
instances, to phosphoric acid or potash or lime, naturally contained 
in the materials of which the roads are made, and set free therefrom 
or made available for the support of plants through pulverization, 
rather than to the comparatively small amount of the dung of animals 
dropped upon the road or to any mere moistening effect produced by 
the water that flows from the road. 
This illustration has value as tending to show how little worth the 
cost it would ordinarily be to pulverize rocks artificially, in order to 
apply their powders as manure; for the wash of roads, and street 
sweepings, though often useful and sometimes valuable fertilizers, can 
in no wise be classed as strong manures, all possible allowance being 
made for the dung in them, and for the water of the wash, as well as 
for their powdery condition. If expressed in terms of money, their 
value would be seen to be exceedingly small, excepting perhaps some 
unusual and quite extraordinary instances. 
The analyses of the sands above given were made in connection 
with experiments upon the growth of plants in these sands. Some 
of the results of the culture experiments have been described already 
in Volume I. pp. 56-63, and the others will be published hereafter. 
Tor the present it need only be mentioned that the indications afforded 
* In his ‘‘ Chemische Feldpredigten,” Leipzig, 1856, 2. 103. 
