REPORT OF THE SUPERINTENDENT OF GARDENS. 201 
fail to succeed where another plant requiring only a trace of the sub- 
stance would maintain a healthy growth. Some plants require much 
potash or soda, some much lime, others a large proportion of silica. 
A rotation which would allow these plants to follow each other in suc- 
cession, or cause one crop which requires only a small quantity of any 
particular inorganic substance to succeed another which requires that 
substance in large amount, would consequently be beneficial. 
Taking these facts as a basis, the theory is propounded that the ne- 
cessity for a rotation of crops is caused by the exhaustion of certain 
inorganic substances which, if supplied in due quantities, would insure 
the successful growth of the same plant on the same soil for an indefi- 
nite period. But in the absence of the knowledge indispensably neces- 
sary for an accurate estimate of the exact quantities required, a system 
of rotation is not only advisable but it is the only resource of the culti- 
vator until science determines the exact specific relations which exist 
between the plant and the soil from whence it receives its food. 
The deductions naturally following the above explanation regarding 
.plant food led to the supposition that chemical analysis would indicate, 
with a great degree of certainty, the exact line of practice to be fol- 
lowed in regard to rotation of crops, or perhaps obviate the necessity 
for any change except that of convenience. This was to be effected by 
analyzing the soil and the plant to be grownin it, so that the ingredients 
removed by the latter could be replaced, and thus the fertility of the 
soil indefinitely maintained. But at present there are no indications 
that such accurate knowledge is forthcoming, neither the analyses of 
soils nor the analyses of plants furnishing the data seemingly necessary 
for practical purposes. 
The phenomena attending the growth of certain crops for a series of 
years on the same soil apparently includes certain factors that are not 
readily explained. For instance, it isobserved that even in the case of 
such humble plants as the petunia and the verbena, if they are con- 
tinued for a few years in the same ground they will cease to give satis- 
faction, even although the soil is annually manured with ground bones, 
rotted stable manure, or other kinds of ordinary manurial applications. 
In flower gardens, when itis desired to grow these plants year after year 
in the same spot, it is found necessary to renew the soil yearly by re- 
moving 6 or 8 inches from the surface and replacing it by fresh earth 
from other sources. 
The same results have been found in the culture of the grape. For 
a number of years past it has been customary for the department to 
propagate several thousands of plants, embracing many varieties, of na- 
tive grapes. These are mostly grown from single eye cuttings in sand 
beds under glass, and placed singly in pots when rooted. About the 
end of May they are turned out of the pots, and planted out in the open 
field rather closely, in rows which are about three feet apart. When 
they have finished growth for the season they are lifted and removed 
from the field; the ground receives a coating of rotted manure, which 
is either ploughed in or worked with a spade, leaving the surface rough 
to be acted upon by the frost. In the following spring the surface is 
again worked over and the soil placed in good order for planting. At 
the proper period young grapes are again planted as before. These are 
removed at the end of the season, and the ground receives similar treat- 
ment to that of the previous year. Notwithstanding this treatment, the 
third crop is very indifferent, and if a fourth successive crop is planted 
it will prove to be an entire failure. 
Experience shows that by selecting a field which has never been oc- 
