THE MODIFIABILITY OF TRANSPIRATION IN 
YOUNG SEEDLINGS 
JosrEpH Y. BERGEN 
(WITH FIVE FIGURES) 
The writer has often noticed the fact that young seedlings (e. g., 
of Cucurbita and Phaseolus) grown under bell glasses wilted almost 
at once when exposed to the dry air of a furnace-heated or steam- 
heated room. Gardeners all know that plants started in cold frames 
must be “ hardened” by gradual exposure to the ordinary atmosphere, 
brought about by lifting slightly the sashes with which the cold frames 
are covered. 
It appeared worth while to investigate quantitatively the rate of 
transpiration of these tender seedlings, grown in an extremely moist 
atmosphere, and the simplest possible case for study seemed to be that 
of annuals, for these cannot be supposed to have inherited a tend- 
€ncy to develop extreme adaptations to an abnormally moist atmos- 
Phere during part of the brief lifetime of the individual plant. Seed- 
lings of the following species were grown in well-watered earth, some 
under glass cases with air-tight joints, and others in the free air of 
a furnace-heated room. 
Cucumis sativus Oxalis corniculata 
Ipomoea purpurea Phaseolus vulgaris 
Lupinus albus Salvia splendens 
Mirabilis Jalapa Sinapis alba 
Nicotiana “Sanderae” 
The temperature was on the average about the same for the covered 
and the uncovered plants; the former, of course, received a trifle less 
light than the latter. The moisture of the atmosphere about the 
leaves naturally differed greatly. Those in glass cases were in a 
_‘Rearly or often quite saturated atmosphere. Those in the free air 
“4 the room were in an atmosphere of which the relative humidity 
during the winter months ranged from 16 to 32 per cent., averaging 
less than 25 percent. This is drier than the average summer atmos- 
Phere of an oasis in the Sahara. Some plants were also grown In 4 — 
“73) [Botanical Gazette, vol. 48 
