74 Hicks on Irrigation of the N'lohrara Valley. 
them, and their stems and leaves expose surfaces which, in the 
aggregate, are so enormous that the loss of water by this chan- 
nel probably exceeds all other losses. It has been found indeed, 
that a plant loses water one-third as fast as a body of water 
whose exposed surface is equal to that of the plant. A field of 
growing crops presents surfaces in the form of succulent stems 
and leaves many times as great as its own superficial area, and 
all these surfaces are exhaling the vapor of water, the loss of 
which must be supplied from the soil. We may safely assume 
that these surfaces are at least three times the area of the field, 
and since evaporation from them is one-third as fast as from 
vv^ater, the loss will therefore be equal to that from a pond of 
the same size as the field. In a dry climate this would be very 
great, but supposing it to be barely one foot over the whole 
surface during the irrigating season, the loss by evaporation 
from plants alone would be 426,888,000 cubic feet of water on 
9,800 acres. To supply this loss would require the whole capac- 
ity of the Niobrara river for fifty days. 
The water absorbed and remaining in the tissues of plants 
must also be considered. If meadow land were irrigated and 
should produce four tons of hay per acre, the grass when cut 
would weigh nine tons, of which seventy per cent. Avould be 
water. For each acre of land 6.3 tons of water would be taken 
up in vegetable tissues an 1 remain vuitil harvest. On 9,800 acres 
61,740 tons would be used up in this way to supply which 
would require the whole capacity of the Niobrara river for six 
hours. 
It will readily be seen that the demands of vegetation alone 
will consume the greater part of the water of irrigation. But 
1:his precisely is what irrigation is for, namely, to supply the 
'demands of vegetation. If I have spoken of the water so used 
as lost^ it is only with reference to its further use upon other 
sections of the same valley. It is not by any means tvasted^ 
though it be "lost" in that sense. 
Some water is also lost by percolation. I refer not so much 
to that which enters the earth along the course of the main 
ditches as to that which has reached the irrigated fields, and 
never returns to the stream because it penetrates to depths below 
its level. That which remains in the earth above the level of 
