TRANSPIRATION. 79 



within wide limits. All the figures which have been published, based upon calcu- 

 liitions or experiments in the laboratory, are useless for jiractical purposes. Espe- 

 cially do those figures which represenb (he rer|nirementof the plant as exceediug the 

 amount of precipitatious, exhibit ou simple reHection, their absurdity. 

 ' If the requircmeut per acre is cousidered, the density of the growth of plants must 

 also be taken into account. 



The first careful and comprehensive investigations into the water requirements of 

 forest trees Avere made by the Austrian furest expt-rimeut stations in 1878 (F. B. 

 Hohnel), and full tables of the results obtained can be found in the records of those 

 stations. 



An average of the many figures there presented would make the amount of tran- 

 spiration per 100 grams of dry weight of leaves in conifers 4,778 to 4,990 grams oT 

 water, in deciduous-leaved trees 44,472 to 49,553 grams of water. That is to say, 

 the deciduous trees transpired about ten times as much as the conifers, and compar- 

 ing the two extremes of transpiration, the deciduous tree with the highest rate of 

 transpiration utilized twenty three times more water than the coniferous tree with 

 the lowest rate. Ash, birch, and linden were found to be the most vigorous tran- 

 spirers, oaks and maples transpiring much less. Curiously enough, while in the 

 conifers shade reduced the transpiration considerably, in the deciduous trees it had 

 the opposite effect. 



During the period of vegetation the following varieties transpired per pound dry 



weight of leaves : 



I'oiiiids 

 of watf r. 



Birch and Linden 600-700 



Ash 500-600 



Beech 450-500 



Maple 400-450 



Oaks 200-300 



iSpruce and Scotch Pine 50-70 



Fir 30-40 



Black Pine 30-40 



The next season, which was more favorable to transpiration, the amounts were 

 larger; the deciduous trees transpiring from 500 to 1,000, the coniferous from 75 to 

 200 pounds, or in the projiortion of one to six. 



The following actual amounts transpired per 100 grams of dry leaves during the 

 third season (1880), will show the relative position of the various species (European) : 



Kilograms. | Kiloiiranis. 



Ash 101, 850 Scotch Pine 12, 105 



Birch 91,800 Fir 9,380 



Beecli 91.380 Austrian Pine 7,005 



Hornbeam 87,170 I Asjien 95,970 



Elm 82,280 j Alder 93,300 



Maple (J. crtWjfjr.sOT) 70,380 {Linden 88,340 



Norway Maple (J . plafa- | Larch 125, 600 



7ioidcs) 61, 180 



Oak {(,>. robitr) 69,150 I Average deciduous trees .. 82,520 



Oak ( Q. Cerrh) 49, 220 Average conifers 11, 307 



Norway Spruce 14,020 i 



The variability of transpiration from day to day is of Avide range; a birch stand- 

 ing in the open and found to have';iO0,O0() leaves was calculated to have transpired 

 on hot summer days 70i) to 901) pounds, while on other days its exhalations were 

 probably not mon; than 18 to 20 pounds. 



A fifty to sixty y(!ar old beech was found to have 35,000 leaves, with a dry w(Mght 

 of 9.86 pounds; a iranspiration at the rate of 400 pounds per pound during the period 

 of vegetation would make the total transpiration 3,944 pounds per tree (about 22 

 pounds daily) ; and since 500 such trees may stand on 1 acre, the transpiration pet 



