46 ANICAL GAZETTE [JANUARY 
have been repeated, with similar results. Some experiments have 
also been made on plants other than Cyperus, but in this paper 
my description will be confined to this plant. 
SAMPSON and ALLEN (26), in studying the influence of external 
factors on transpiration, have found that “variation in the tran- 
spiration per unit area for a given time is found to be slight for 
plants of the same species, when about the same age, and grown 
and tested under similar conditions’’; facts which my observations 
on Cyperus fully substantiate. 
The following table (I) shows the variation in the total daily 
amount of water lost in Cyperus plants of nearly the same age and 
size when grown and tested under our greenhouse conditions. 
The 5 plants in each series were selected with reference to likeness, 
and the weighings were made at the same time for ro days, the 
average of which was taken as the average daily transpiration 
loss. The average daily temperature was calculated from the 
daily record of a self-registering R1cHarp thermograph placed in the 
neighborhood of the plants. This is necessary, since the changes 
in temperature affect the transpiration rate to a very marked — 
degree. The plants in series I were young, with their involucral — 
leaves just expanded; those in series II were well developed, dark- 
green plants. 
See tao) ca eee Ts, 
TABLE I 
SHOWING VARIATION IN AMOUNT OF WATER LOSS BY PLANTS OF APPROXI- 
MATELY THE SAME AGE AND SIZE 
= 
Series I Series IT . 
aoa 
| Average daily Average daily : daily p 
No. of exp. | water loss in nresees daily | No. of exp. water toss i in poem : 
grams perature gram 
Boers. 
1 SSR rats 4.5 24° C I 1.8 20° C. 
pH ee ei 4:7 24° C 2 1.9 ae C. 
Bese 5-0 24°C 4 1.6 ay C. 
Ra ee 4-6 24°C 4 2.0 ~ - 
ge ee 4.2 24° C 5 1.7 ate: 
kee 
I have determined by the pot method and by means of plants - 
grown in nutrient solutions that the average amount of watet 
transpired per unit area for a given time is 4-10 mg. per sq. cm. Pt 
hour during a period of 24 hours. In comparison with the earlier — 
