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rgtt] OVERTON—TRANSPIRATION AND SAP-FLOW 47 
observations of SAcus on the amount of transpiration in Helianthus 
(about 2.23 mg. per sq. cm. per hour) and with those of more 
recent investigations, it is evident that Cyperus may at least be 
regarded as a rapidly transpiring plant under greenhouse conditions- 
Miss CLapp (6), in comparing a number of common plants as to 
transpiration, found that Helianthus annuus stands far ahead of 
the 30 other forms which she investigated. A plant with a total 
leaf area of 5.056 sq. cm. gave off on the average 25.7 mg. of 
water for each sq. cm. of leaf surface per hour under ordinary 
greenhouse conditions. Hence Cyperus gives off a much smaller 
amount of water per unit area of leaf surface per hour than does 
Helianthus. 
The leaf stems have numerous stomata over their surfaces, 
while these structures are confined almost entirely to the under 
surfaces of the leaves. By removing the involucres of plants 
grown in nutrient solutions and sealing the cut ends of the stems 
with grafting wax, then making weighings, the daily transpiration 
per unit area of stem surface was found to be on the average about 
3-5 mg. per sq. cm. per hour. After having measured the average 
- daily water loss of a plant in culture solution through its leaves 
and stems, the involucre was removed, the cut ends sealed, and 
weighings resumed for several successive days. 
TABLE Ht 
SHOWING AMOUNT OF DAILY WATER LOSS sti A PLANT BEFORE AND AFTER 
MOVING THE LEAV. 
PLANT WITH LEAVES PLANT WITH LEAVES REMOVED 
D Daily loss in | Average Daily loss in Average 
sai grams telpetatnve Days grams temperature 
2 17 4 ae C, I 2.2 25° 
Yeas Gs 19.9 25° C. 2 2.2 23 | <. 
Oe era 18.1 a4 C. 3 2.1 as C. 
Fag, Oe 18.6 24° C. 4 | 2.2 25.C 
See teery <. 19.4 a5 s 2.2 a5 C 
ONE a MEE og 
Average daily transp. loss 18.68 grams | Average daily transp. loss 2.18 grams 
The data tabulated in table II were obtained by using a large, 
_ well rooted plant growing in a nutrient solution. The stem was 35 
_ cm. long, 4 cm. in diameter, bearing an involucre of 17 large rays. 
