JANUARY 26, 1912] 
stood, but it may be stated that CaCl,, BaCl, and 
SrCl, bring about visible changes in the plasma 
membrane which are quite different from those 
produced by such salts as NaCl, and it is hoped 
that a further study of these visible changes may 
throw some light on this question. 
Observations on Evaporation and Transpiration in 
Prairie and Forest: B. SHIMEK, Iowa State 
University. 
In an effort to determine the differences between 
forest and prairie plants which would account for 
their distribution, observations were made on the 
transpiration of certain forest and prairie plants 
in their native habitats and in transposed habitats. 
To illustrate the plan and purpose of the work two 
sets of plants are taken. In one of these cases 
Phryma leptostachya L. from the forest and 
Kuhnia eupatoroides var. corymbulosa T. & G. 
from the prairie were compared, and in the other 
Anemone virginiana L. from the forest and Ver- 
bena stricta Vent. from the prairie were employed 
for the same purpose. 
Two stations were selected on a ridge near Iowa 
City, one side of which is prairie and the other 
forest, one station being located in each. The 
plants, which were as nearly as possible equal in 
size and vigor, were cut and inserted into bottles 
of water, which were sealed. Two plants, one 
from the forest and one from the prairie, were 
placed at each station, and the loss of water was 
determined at two-hour intervals. 
In addition to this, observations were made at 
each of the stations on evaporation, and the 
meteorological conditions affecting it. The latter 
observations showed substantially the same rela- 
tive results for prairie and forest as those previ- 
ously published by the writer. 
The results may be briefly summarized as fol- 
lows: 
The Phryma in the forest lost 1.9 gram, while 
that on the prairie lost 4.65 grams. The latter 
transpired very actively until it began to wilt, and 
then transpiration declined very rapidly, the plant 
soon becoming dry and crisp. The Phryma in the 
woods scarcely showed signs of wilting. 
The Kuhnia in the forest lost 7.16 grams and 
remained perfectly fresh. That on the prairie lost 
11.13 grams, and was also fresh at the close of 
the experiment. The diminution in transpiration 
in the forest was probably due in part to dimin- 
ished activity on account of less intense light. 
The Anemone lost 3 grams in the woods and 
4.89 grams on the prairie. 
SCIENCE 
157 
The Verbena lost 6.58 grams in the woods and 
27.4 grams on the prairie, transpiration in the 
woods declining in mid-day, being greater at both 
extremes of the day. The decline on the prairie 
in both cases was uniformly quite rapid. The 
greatest transpiration occurred in all cases just 
before wilting began. 
The general result shows that transpiration and 
evaporation are not coincident. 
Shade as a Factor Influencing Evaporation: G. P. 
BuRNS, University of Vermont. 
There is a general belief among some ecologists 
that the evaporating power of the air is the most 
satisfactory summation of the atmospheric factors 
controlling plant distribution. 
In forest nurseries it is the usual practise to 
grow young pine trees in beds covered with racks 
whose sides are either wood or heavy paper and 
whose top is covered with lath. Every other lath 
is nailed, the free lath being later removed to 
produce ‘‘half-shade.’’ 
During the summer a study of the condition in 
the seed-beds has been carried on. The results as 
shown by the Livingston atmometer are given 
below. 
Numerous stations were established representing 
all of the conditions found in nursery practise and 
in the adjacent forest areas. The control station 
was located in the nursery in a very large wire 
cage. The average amounts of daily evaporation 
from the various stations were as follows: control 
45 ¢.c.; full-shade 19 ¢.c.; half-shade with solid 
sides 20 ¢.c.; half-shade with wire sides 43 e.c.; 
pine woods 16 c.c. Of these amounts from 17 per 
cent. to 25 per cent. is lost during the twelve 
hours 6 P.M.—6 A.M., the remainder during the time 
between 6 A.M. and 6 P.M. 
The data gathered seem to show that the 
shading of young trees is a matter of evaporation 
rather than a matter of light, as is generally stated 
in the literature. The final word, however, must 
be spoken as a result of experiment. 
The Investigation of a Climatic Gradient: For- 
REST SHREVE, Carnegie Institution. 
The Santa Catalina mountains, in southern Ari- 
zona, rise from the desert plain at 3,000 feet alti- 
tude to a height of 9,100 feet. The lower slopes 
are characterized by desert vegetation, the middle 
altitudes by chaparral, the higher by coniferous 
forest. The influence of slope-exposure is such as 
to make the vertical limits of these zones and 
their component plants about 1,000 feet higher on 
