676 
Analyse* of Asites of Plants. 
exhausting tban wheat or barley ; barley and oats, however, 
require a much larger amount of silica tban wheat ; of course we 
speak of the grain only, not having yet had opportunity to make 
analyses of the straw of lhe=e crops. The exhausting character of 
a crop should be viewed in two lights. In the case of wheat, for 
instance, the immediate exhaustion is due to the ash removed in 
the whole crop, and to which, of course, the straw and chaff»con- 
tribute very largely ; but in the ordinary routine of farm practice 
this loss is made up by the manure applied, which (if no unusual 
waste occurs; will represent the inorganic matter of the straw and 
chaff ; there is, however, in addition to this, a permanent loss to 
the soil in the removal of the grain ; and it is of this that we speak 
in comparing barley and oats widi wheat. At tlie same time we 
must remark, that from some analyses made by one of us, and 
detailed in Dr. Daubeny's paper on the rotation of crops, it would 
not appear that the straw of barley is less exhausting otherwise 
than in coisequence of its quantity being less than that of wheat 
straw. 
The analyses of barley and oats here given we do not consider 
bv any means sufficient to warrant us in drawing any very decided 
conclusions respecting the mineral history of these crops ; we shall 
therefore reserve any further remarks upon them till a future 
time. 
The ash of rye resembles that of wheat in most respects : if we 
mav judge, however, from the single analysis detailed (Spec. 75), 
it contains a larger amount of silica. The quantity of ash is low 
when compared with wheat, and the crop would consequently be 
less exhausting, as regards the grain, than any other of the 
cereals. 
Of the Method of supplying to the Land the Mineral Ingredients 
of the Wheat Crop. 
We may fairly conclude that, in round numbers, an average 
crop of wheat would remove from the soil in the grain, straw, and 
chair per acre, 
84 lbs. of silica. 
20 lbs. of phosphoric acid. 
4 lbs. of sulphuric acid. 
8 lbs. of lime. 
6 lbs. of magnesia. 
1 lb. peroxide of iron. 
23 lbs. of potash, 
lb. of soda. 
Of these substances three may be coi\sidered as iioU'essentials: 
these are, the lime, the peroxide of iron, and the soda, all of which, 
if the plant requires them, it may re*Jily obtain from almost any 
