120 PLANT LIFE ON THE FARM, 
average, to four to five tons with farm-yard manure, 
and to six to seven tons with mixed mineral and am- 
monia, The tendency to disease, however, increases with 
the higher manuring, in larger proportion than does the 
produce. 
The data of science on the effect of manures must, 
however, only be taken as indications by the practical 
farmer, who must be guided by financial considerations 
and local conditions, in determining what it is best for 
“him to do under particular circumstances at any given 
time. 
An interesting circumstance may here be mentioned, 
viz: that many of our cultivated plants, such as cab-. 
bages and mangold wurzel, have sprung from wild plants 
growing by the sea, and are hence especially benefited by 
the use of salt as a manure. Onions, the growth of 
which is also favored by salt, probably originated from a 
wild stock growing in salt desert regions. 
Fallow.—The good effects of this may be judged from 
the results of some Rothamsted experiments, in which 
the produce of wheat is recorded, after bare fallow, com- 
pared with that of wheat grown continuously on the 
same soil, without the intervention of fallow, and equally 
without manuse. Under such circumstances, the aver- 
age produce for twenty-five years after fallow has been 
eighteen bushels per acre, as contrasted with an average 
of twelve bushels where the wheat has been grown con- 
tinuously. The weight per bushel was the same in both. 
cases. The average quantity of straw after fallow was 
one thousand seven hundred and eighty-six pounds, as 
contrasted with one thousand two hundred and twenty- 
one pounds, where the crop was grown continuously. 
Rotation.—The practice of rotation of crops is amply 
borne out by what occurs in nature and by. chemical ex- 
