a a ea ee ee 
1896.] Anatomical and Physiological Researches. 29 
mostly through the stomata. A number of trees inhabiting 
damp soil were also found to be unable to regulate transpira- 
tion, viz., Betula alba, Alnus glutinosa, and various species 
of Salix; also the shrub Hydrangea hortensis, so thoroughly 
examined by Wiesner. 7? 
“The ability to close the stomata, however, under condi- 
tions unfavorable for assimilation is surely very common with 
plants, which in their native locality frequently have to battle 
with a transient scarcity of water.” An hermetic closing of 
the stomata is especially common with plants whose vegeta- 
tion is interrupted by long periods of rest. Cobalt tests made 
October 20th showed a complete closing up of the stomata 
in Buxus sempervirens, Mahonia aquifolium, and Zaxrus bac- 
cata. They were still open in /lex aguifolium and Hedera 
helix. 
Evergreen leaves which have discontinued stomatory trans- 
piration will not redden the cobalt paper even after they 
have been exposed for a long time in a hot moist room to the 
sun. For example vigorous branches of Buxus, Mahonia, 
Ilex, Hedera, and Taxus were cut off in sunny frosty weather 
Dec. 12th. The cut ‘surfaces were immersed in water and 
the branches exposed in a moist atmosphere to the sun. The 
cobalt test after three hours showed a loss of water only in 
Ilex aquifolium. After eight days Taxus and Mahonia be- 
gan to show loss but Buxus and Hedera still kept their stom- 
ata closed. Of all these evergreens, Ilex is the one that suf- 
fers first from the cold. Stahl confirms the earlier observations 
that in colored autumn leaves the stomata are closed. He 
agrees with Wiesner that the reduction in transpiration greatly 
influences the defoliation of deciduous plants. 
Il. Role of the stomata in the exchange of gases during as- 
simtlation. 
*Sitzungsber. der Kais. Akad. d. Wiss. in Wien. 96: 182-214. Je.-D. 1887. 
