HoUdion of Crops. 
635 
straw to grain, and a proportionally larger amount of the total 
carbohydrates accumulated in the straw, we have in it a still 
larger proportion of the total potash of the crop. It is, however, 
to be borne in mind, as has been pointed out, that the straw ot 
both barley and wheat frequently contains, besides the mineral 
constituents actually essential for the organic formations and 
changes, a more or less surplus amount taken up as the result 
of liberal supply, and retained by the plant. 
Although there is doubtless clear foundation in fact for the 
conclusion that the rule of phosphoric acid is more in connection 
with the formation and activity of the nitrogenous bodies, and 
that of the potash with those of the non-nitrogenous compounds, 
yet it is obvious that in such a view we have only a partial and 
imperfect explanation of the function of these mineral constitu- 
ents. Thus, in the case of the beans there was, consistently 
enough, much more phosphoric acid in the corn than in the 
straw — that is, the more where there was the more nitrogen ; but 
there was also by far the larger proportion of the potash accu- 
mulated in the corn, although the greater part of the dry matter 
of the crop, and with this of its carbohydrates, was in the straw. 
Indeed, although the leguminous crops are pre-eminently highly 
nitrogenous, a liberal supply of potash is essential for their 
luxuriance ; whilst they contain a higher proportion of it in their 
dry substance than do the cereals, with their higher proportion 
of carbohydrates. 
Reference to the figures shows that the application of super- 
phosphate, without potash, enabled the wheat plant, whether 
grown in rotation or continuously, to take up an increased, but 
not a much increased, amount of potash, compared with that in 
the unmanured crops ; and that the direct application of it in- 
creased the assimilation of it still further, though the increased 
amount of it stored up represented only a small proportion of 
that supplied in the manure. 
Without manure, the rotation wheat crops contained an 
average of about 27 lb. of potash, but the continuously grown 
ones scarcely 13 lb., or only about half as much. With super- 
phosphate, without potash, the rotation crops gave an average 
of nearly 30 lb., and the continuously grown ones little more 
than 15 lb.; or, again, only about half as much. That is, when 
the growing crops had to rely for their potash exclusively on the 
stores of the soil itself, the rotation crops took up about twice 
as much as the continuous. Lastly, with the mixed manure 
supplying potash, the rotation wheat crops gathered nearly 36 lb. 
after fallow, but about 38 lb. after the leguminous crops ; whilst 
the continuously grown ones yielded an average of only about 
