164 On the Transpiration of Plants. [ March, 
Plant No. 1 employed, was a common Calla (Calla :thiopica), 
an herbaceous plant 3 feet 114 inches high. Its whole weight on 
taking it up, with roots cleaned, was 2 pounds 2 ounces; weight 
of evaporating portion, or all above ground, I pound 3 ounces, 
240 grains in a green state; complete weight of outfit, including 
plant, vessel, and apparatus adjusted for experimentation, 21 
pounds 4 ounces 20 grains. This latter weight is here stated in 
order to avoid an unnecessary record of figures in the table of re- 
sults to follow, by giving the weight of the growing plant at each 
time it was taken. Suffice it to give the loss of weight, or its 
equivalent the amcunt of water evaporated during the periods of _ 
time indicated. The same plan will be pursued hereafter. 
The following are the results with this plant : 
Duration Loss of weight or 
Ex, F seaaesanitng amount evaporated, Place. Weather. 
| PEA 2a 
I) 12 hours, day. 1420 gr. Indoors. Clear. 
II 12 ai 195 s Cloudy, rain. 
HU 12 s 1440 “ 1 Clear and warm. 
IV} 12 X 2040 “ In open air. Paty slöndy: 
| 12 ee 2380 “ “ec Cle 
VII 12 “ S320 s “ Cier, windy. 
The important part played by the sun’s rays and atos pie 
currents in transpiration is very well shown by these results. The 
plant while indoors received the sun’s rays only about half the 
time during a clear day, which was the case in all indoor experi- 
ments made, and, although the room in which it was kept was 
well ventilated, the currents were in no way comparable to the 
circulation of the atmosphere outside. It was found, very curi- 
ously, that this plant evaporated nothing during a cloudy night in 
or out of doors, and only about 460 grains on an average during 
clear nights in open air. 
Plant No. 2 was one of our common geraniums (Pelargonium. 
cucullata); also herbaceous; 18 inches high; weight in a green 
haling part 7 ounces; complete weight fitted for experimenta- 
tion, 9 pounds 15 ounces 350 grains. The evaporating surface 
of the two first plants tried was not estimated on account of the 
shape of the leaves, and the extent of the branches in the case of 
the geranium and of the leaf stalks in the case of the calla (which 
it would have been necessary to include) rendering it too difficu 
_ for the observer. It might be well to state here that the plan 
