Igtt] . OVERTON—TRANSPIRATION AND SAP-FLOW 49 
therefore, the rate of sap-flow in Cyperus is exceedingly rapid. 
Certain other herbaceous plants, however, have been reported as 
having a still more rapid flow, STRASBURGER observing that the 
rate of rise was 6 m. per hour in Bryonia and Cucurbita. We see, 
therefore, that Cyperus may at least be regarded as a rapidly 
transpiring plant, that its transpiration stream is correspondingly 
rapid, and that the amount of water given off from plants of rela- 
tively the same age and development show very little variation. 
Experiments with heat 
Over 200 experiments in which portions of the stems were killed 
with steam have been performed and the results carefully com- 
pared. The results of all of them are substantially in accord. 
The results obtained in several representative experiments are 
tabulated in table IV. 
In table IV the numbers in the first column on the left refer 
to the actual numbers of the experiments performed; for example, 
6—S (1908) means the sixth experiment in 1908 in which a 
portion of the stem (20 cm. in this case) was killed with steam. 
Each year the experiments performed were numbered anew. In 
the second column the length of the stem from the soil to the invo- 
lucre is tabulated. Thé length of the steamed portion varies from 
a minimum of 5 cm. to a maximum of 30 cm., as will be seen from 
the third column; the time of treatment was 10-30 minutes. In 
the fourth column the actual day and month when the steam was 
applied are shown. The plants were in all cases grown in pots in 
soil under favorable greenhouse conditions. The control plants were 
stems cut from the same pot as the one which had been treated, and 
were approximately of the same size and age. They were set in 
water in the neighborhood, and the time of wilting of the leaves 
compared with those of a killed plant. As is well known, the leaves 
on cut stems of this plant not placed in water wither within 24-48 
hours. I have omitted from this table the distance above the 
base of the stem at which the steam was applied, since I have 
found that it makes no appreciable difference whether it is applied 
near the leaves or lower down. 
It is plain that the leaves of umbrella plants which have a portion 
