Me | tion of the sun’s rays, is shown by the fact (bat, during tie z 
170 On the Transpiration of Plants. [March, 
. The following table, compiled for the number of clear days, 
will serve to exhibit the average rate of transpiration by day which 
took place in the open air during clear weather. It will also in- 
dicate the relation between leaf surface and the weight of the 
plant, and amount transpired. 
The mean temperature and average dew point have also been 
recorded in the table. 4 
No.| Name of Plant. | Duration of Average Evaporating Weight of | | Average lA verage 4 
experiments evaporati n surface. plant. |temp’ture, laew point. ; 
e a cea 12 hours. 2850 gr. All parts mai n lb. 2 oz.] | sno 
2 |Geranium FES aR Teas es ok 4 14420 Be sates Ho : 
3 |Fuchsia..... s ya “ /450 sq. in |1920 “ 64:59 | -49:6°. ; 
4 ret s # aB V aa S 2170 “ 73 2] 56.7 i 
5 [Camellia . ey TO RAI OS Ca tae a's 75-5 63.3 ; 
6 | Lantana. .... ee 17175 “ “|330 «“ 720 “ 75.1 | 61.7 o 
7 |Dracena.... “ ese OO S ee -Isg 62. 
After an inspection of this table, the average rate of evapora- 
tion for soft, thin-leaved plants, in clear weather, may be put down : 
at about 114 ounces per day (12 hours) for every square foot of — 
leaf surface. The Lantana shows nearly 2 ounces to the square 
foot of surface. The Camellia, with its dense, smooth leaves, | 
averaged less than half an ounce to the square foot of surface, per — 
day. : 
The nature of the leaf structure modifies very greatly the rate 
of evaporation, as may be seen by comparing the results fromthe — 
Camellia with those of other plants having soft and thin leaves. 
Apart from structural peculiarities, no doubt the sun’s rays 
stand first in importance among the modifying influences; for a 
going back to the results from the Fuchsia, for instance, we find 
the average temperature higher and the dew point greater during i 
the indoor experiments than when the plant was exposed, and — 
yet the relation of evaporation in the two situations was, other 
things being equal, about as ordinarily the case. The same ob 
tained in the case of the Hydrangea in a still more marked de- 
It j is still an unsettled question whethes radiation, as such, pro- 
duces this great effect, or whether it is through’ the heat that ac 
companies the rays, or the chemical changes they produce. 
That the difference between indoor and .out of door evapora- 
