128 BOTANICAL GAZETTE [AUGUST 
ing other differences that may be passed over at present. The capi- 
tal fact, however, is that this species, whether as seedling or mature 
plant, exhibits an endurance of extremes in the matter of water sup- 
ply that apparently vety few species not possessing a storage system or. 
its equivalent have attained. 
This ready adjustment to differences of water supply, manifested 
not only in power of endurance but also in rate of growth and in 
other particulars, might naturally be expected to find expression in a 
corresponding varying rate of transpiration; it becomes, therefore, 
a matter of special interest to determine the habits of the creosote 
bush in this respect, particularly after long periods of drouth. Accord- 
ingly a series of experiments were conducted in which the hygro- 
metric method of determining transpiration, suggested by Dr. D. T. 
MacDoveat was chiefly employed. By permission of the Desert 
Laboratory some of the results are here given in advance of publi- 
cation elsewhere, in which a full account of methods employed by 
Dr. W. A. Cannon will be given by him. 
At the time these experiments were undertaken, late in April 
extremely dry conditions, both of atmosphere and soil, had long pre- 
vailed. The rainfall since September 1903, a period of nearly seven 
months, had aggregated only one inch, spring flowers had failed to 
appear, and during nearly all of the winter and spring an intolerable 
dust had filled the roads and risen into the air. Under such circum- 
stances it might naturally be expected that transpiration on the part 
of every plant not artificially watered would be reduced to a minimum; 
the facts of the case, however, by no means warrant this conclusion. 
Two specimens of Covillea were selected, one on the hill a little 
to the northward of the laboratory, the other at the foot of the hill in 
the same direction. The former presented the fresh appearance 
exhibited by most of the creosote bushes near the laboratory, indica- 
tive of a water supply, however limited, in excess of that in the plain 
below, where the bushes looked dull and dried-up, as if subjected to 
Most severe conditions, to which it seemed as if they must succumb. 
This consists essentially in direct reading of a specially constructed hygrometer 
Placed with the plant under a bell-jar, from which escape of moisture is prevented . 
oiled silk or a cement base. The correction for vapor-pressure is made once for 4 
by weighing calcium chlorid before and after the saturated air of the bell-jar has a 
Passed through it. 
