Transpiration Current in Submerged Water-plants. 637 
We also hope by further experiments to obtain some light on the 
mechanism of the rapid water current in P. lucens , and in other submerged 
water-plants. Some preliminary experiments have indicated that it 
depends principally on the leaves : 
1. When the apex of a detached stem was removed the eosin entered 
from below more slowly than before, in one case 4*5 cm. in three minutes. 
When the bulb of eosin was affixed to the upper cut end a very slow 
current was observed in the reverse direction. In one experiment it was 
found that after eight hours the eosin had travelled backwards throughout 
the length of the detached stem employed. In two other experiments, 
lasting three minutes the eosin had traversed a distance of about 1 cm. 
When bulbs of eosin were attached to both cut ends, the eosin penetrated 
slowly from each end. 
The possibility of a reverse current suggests that the normal current 
depends at most only to a very small extent on the stem itself. 
1 . That, on the other hand, the leaves are the determining factors is 
indicated by experiments in which some or all of the leaves were removed. 
When all the leaves and the apical bud were cut off the current in the 
upward direction was extremely slow, e. g. in one experiment, 3 cm. in 
thirty-two minutes. In the backward direction the eosin had not penetrated 
at all at the end of an experiment lasting eight hours. When some of the 
leaves were removed, the current was diminished roughly in proportion to 
the number removed. For instance, in an experiment in which about half 
the leaves were removed the rate of transmission of the eosin was 3 cm. per 
minute as compared with 6 cm. in a control experiment with a similar 
branch. 
On anatomical and experimental grounds, Sauvageau, 1 Weinrowsky, 2 
and Max v. Minden 3 point to special apical ‘ pores ’ as organs of exudation. 
From experiments in which the tips of the leaves were removed these do 
not appear to be active , as the results showed no appreciable diminution in 
the current ; but we do not regard these experiments as conclusive. 
In conclusion, our experiments have shown 
1. An unexpectedly rapid water current in detached rootless stems of 
Potamogelon lucens ; 
4. That this current is at any rate largely dependent on the leaves. 
Botany School, Cambridge, 
August , 1909. 
1 Sauvageau, 1 . e. 
2 Weinrowsky, P. : Untersuchungen liber die Scheiteloffnungen bei Wasserpflanzen, Bot. 
Centralbl., Beihefte, ix, 1900, p. 176. 
8 Minden, Max v. : Beitrage zur anatomischen und physiologischen Kenntniss wasser- 
secernierender Organe. Inaug.-Diss., Bonn, 1898, 
