TRANSPIRATION. 39 
Pounds of Water. 
Bireli sand Mindemecco-te eek sea eae netieece aw eules 600 to 700 
ASSlliie <3 oimieecetutine> waePniee eum eat leat nk Nin eat 500 to 600 
HE Nc Let I hatin teed AN ede pm we OC RIEU EO 450 to 500 
Maple wearin een ener ns tre tan oan eens: 400 to 450 
CY ata errs Rese rata ROR ANY OS Tucan Wah ae ech VAP ESA 200 to 300 
Spruce and “Seotely Pitiéw,.occccayescosiehes ae 50 to 70 
IAT Sa Sicse es semen ane ees Aptaapn btn ae apa dener Tee hain) Suan = GOAL: AO: 
1B} Wet baal 2h al nema ee Rare fe cree CNyt a Nam as 30 to 40 
Average, deciduous trees..............-.0 000s 470 
Average, evergreen trees........ 0.0000 c see eee 43 
This shows that there is a great difference in the amounts of 
water transpired from deciduous trees and evergreen trees. In 
this case the deciduous trees transpired about eleven times as 
much as the evergreens. 
“The variability of transpiration from day to day is of wide 
range; a birch standing in the open and found to have 200,000 
leaves was calculated to have transpired on hot summer days 
700 to 990 pounds, while on other days its exhalations were prob- 
ably not more than 18 to 20 pounds. 
But while trees transpire large amounts of water, our agri- 
cultural crops and other low vegetation transpire much larger 
amounts to the same areas. A small factor in the dissipation 
of water supplies is the amount of water that is retained in the 
plant itself. As before mentioned this may amount annually 
to about 5,0co pounds per acre. The water in fresh cut woods 
forms a large part of their weight. In hard woods, such as Ash, 
Oak, Elm and Birch, it forms 38 to 45 per cent, and in soft 
woods 45 to 55 per cent or more. 
ELEMENTS OF CONSERVATION OF WATER SUPPLIES. 
In discussing the elements of dissipation as to the degree of 
their effect under forest cover as compared with the same ele- 
ments at work in the open field, we have seen that the shade, 
the low temperature, the relative humidity, the absence of strong 
air currents and the protective and water-holding capacity of 
the forest floor are all factors in the conservation of the water 
supplies. We have also seen that the quantity of water lost by 
evaporation, the greatest source of dissipation, may be more 
