A74 RETURN OF MATERIAL TO THE HOP ROOT. 
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The amounts removed by the whole plant are not unlike 
the quantities taken from the soil of an average crop of 
swedes ; they are roughly equivalent to 5 cwt. of Nitrate of 
Soda, 6 cwt. of Kainit, and 2 cwt. of Superphosphate, per 
acre. It must not be supposed, however, that the above 
mixture represents the amount or proportions of manure to 
use for the crop, for it often happens that the particular 
constituent least abundant is that which the plant finds a 
special difficulty in obtaining from the soil, and of which it 
most wants an extra supply as manure. 7 
The amount of dry matter produced per acre affords a 
slight indication as to the amount of water required by the 
hop plant, for the researches of Lawes and Gilbert, 
Heliriegel, King, and Dr. H. Brown, have furnished figures 
showing the relation between the amount of water that is 
transpired by a plant, and the amount of dry matter formed, 
and though no figures are yet available for the hop plant, a 
fair approximation can be obtained by taking the average 
figure of 300 lbs. of water transpired for each pound of dry 
matter produced. The dry matter produced being 3,7 85 lbs. 
per acre, or 1'°7 tons, the amount of water required will be 
510 tons per acre, or a little more than 5 inches of rain must 
pass through the hop plant during its growth. The water 
required by the crop is thus not very large, being about 
the same as that needed by a good crop of clover or seeds, 
but much less than that which is requisite fora crop of roots, 
especially of mangolds, and this enables one to understand 
how such great crops of hops can be grown in East Kent, 
a district of small rainfall and extreme evaporation. 
By comparing the analyses of the bine and leaves at picking 
time with the corresponding material when the plant has 
ripened and died, it will be seen that there has been a con- 
siderable migration of the valuable constituents to the root. 
In the dead bine the proportion of nitrogen is only about one- 
third of what is present when the plant is growing, while the 
potash andthe phosphoric acid have been still more thoroughly 
removed. In the case of the ieaves the comparison is more 
difficult to make, since the dead leaves have lost by decay and 
weather much of their softer combustible material. This is 
