632 
Rotation of Crops. 
fixed. Further, whilst in the turnip-crop there was several 
times as much dry substance in the roots as in the leaves, in 
the barley there was even more dry organic substance in the 
straw than in the grain. Again, in both crops, by far the larger 
proportion of the dry substance consists of carbohydrates — in 
the one chiefly sugar, and in the other almost exclusively starch 
and cellulose — the latter making up by far the greater portion 
of the dry substance of the straw. It is obviously quite con- 
sistent that under these circumstances there should be more of 
the total potash of the barley crop accumulated in the straw 
than in the grain. It must at the same time be observed that, 
whilst the potash in the grain is comparatively fixed and bears 
a fairly uniform relation to the amount of di'y substance, the 
quantity which remains in the straw is subject to great varia- 
tion in proportion to the dry matter, according to the variation 
in the supply of it within the soil — a great excess above the 
amount in other cases being sometimes found in the straw. 
Indeed, the figures show a considerably greater proportion of 
the total potash of the crop accumulated in the straw where 
there was a liberal supply of it in manure. 
Referring to the amounts of potash taken up in the rotation 
barley crops on the different plots, according to the manuring or 
other treatment, the figures show that there was not much dif- 
ference between the amounts without manure and with super- 
phosphate alone. There was, however, distinctly more taken 
up on the portions of the superphosphate plot where the roots 
had not been removed than where they were ; and where, there- 
fore, there was conservation for the succeeding crop. With the 
mixed manure, however, with its supply of potash as well as of 
phosphoric acid and nitrogen, the amount of potash in the crops 
is greatly increased, the increase corresponding closely with the 
increased amount of produce. 
Lastly in regard to the potash, whilst without manure and 
with superphosphate alone the rotation barley has gathered 
much more than the continuously grown, with the mixed 
manure and full supply of all constituents, the amounts of 
potash taken up were, as were those of nitrogen and phosphoric 
acid, nearly the same in the rotation and the continuous crops 
where in rotation the preceding roots had not been removed ; 
but where they had been removed, the amounts of potash in the 
succeeding barley were less, as were the crops themselves. 
The Potash in the Leguminous Crops . — Of all the mineral 
constituents of the crops, perhaps potash and lime are the most 
generally recognised as having some distinctive effects when 
applied as manure for leguminous crops. We have now to refer 
