28 The Botanical Gazette. [January, 
leaves and in fact in all cases where the stomata were closed 
on account of an insufficiency of water in the plant even 
though they were exposed to the sun, no reddening of the paper 
occurred. This shows how very small the evaporation is 
through cuticularized epidermis even when exposed to the 
bright sun. The same was found to be true with fully tur- 
gescent leaves supplied with water. 
2. Regulation of transpiration by means of the guard-cells. 
—Stahl confirms the observation of Mohl, Leitgeb and others 
that in the wilting of a leaf the guard-cells are the first to be 
affected by the loss of water. When two leaves as nearly 
alike as possible except that one is slightly wilted and has the 
stomata closed, are placed together between two pieces of 
glass and the upper surfaces exposed to the bright July sun, 
the one with the stomata closed gives off no water and wilts 
no further while the turgid one with open stomata at the start 
discolors the cobalt paper rapidly and becomes completely 
wilted. This was found true in all cases investigated, viz., 
leaves of Tropacolum majus, Tradescantia zebrina, Pharbttis 
hispida, Pelargonium zonale, Rhus cotinus. Rapid wilting 
also occurs when freshly picked leaves are exposed to bright 
sun in highly saturated air, while leaves which were first 
slightly wilted so that their stomata are closed lose no more 
water when exposed to the sun. Sometimes the stomata 
would open again in the saturated air and then transpiration 
would continue. 
These experiments show that stomata do not close in sat- 
urated air even though the evaporation from the leaf has led 
to its complete wilting. They further indicate that as the 
stomata open widest in bright sunlight and saturated air that 
€vaporation under these conditions may be much greater than 
we expect. Haberlandt’s observations on tropical plants‘ 
(viz., that they lose two or three times less water than plants 
in Germany) may be even very short of the reality for plants 
removed from the direct influence of the sun. On the othef 
hand those exposed to the direct sun probably lose more that 
Haberlandt found. Stahl found that many marsh plants and 
shrubs in the damp tropical forests are unable to close theif 
stomata. When exposed to dry air they dry up in a few 
hours. It was also found in these cases that the loss wa | 
| 
| 
] 
*Haberlandt, G. Anatomisch-physiologische Untersuchungen iiber 43° 
tropische Laubblatt. Sitzungsb. d. Wiener Akademie 101: 785-816. O. 189% 
