152 BOTANICAL GAZETTE [AUGUST 
seeks to extend our knowledge of hydrodynamics. He examined the cohesion 
of water by means of the supersiphon, i.e., a siphon whose legs are so long 
as to permit the use of columns of liquid too high to be raised by atmospheric 
pressure, to which (STEINBRINCK thinks erroneously'?) the action of the common 
siphon is ascribed. e attempted to ascertain the cohesion of water under 
various conditions, and met sometimes with such capricious behavior of his 
apparatus that, more than ever by this experience, he is convinced of the necessity 
for much more extended physical knowledge before the problem of the ascent 
of sap can be solved. The reinvestigation of the tension of gases in fern and 
other sporangia (which he finds nearly at atmospheric pressure) and of their 
disappearance when the sporangia are wetted, shows that these phenomena do 
not fall in with any known physical laws; and as these structures plainly contain 
only dead cells the problem cannot be obscured by dragging in “vital activities” 
and remains at present inexplicable. How much more caution, then, is neede 
in the more complex problem of sap movement! 
STEINBRINCK finds that a water filament 2™™ thick, moving at the rate of 
2m per second, bears a pull of four atmospheres, its tensile strength increasing 
with diminishing size and rate of flow. Such filaments bear even violent shaking, 
0° to 35° C.). By ingenious experiments he shows that cohesion may act through 
membranes, such as the partitions that interrupt the tracheae. As for therobjec- 
tion to the cohesion theory on account of the Jamin-chain condition, he suggests 
caution on account of deficient physical knowledge, enforcing this by citing the 
case of gas absorption in the opening sporangia already alluded to. He does 
not deny the participation of living cells, but can form no conception of the 
manner in which they act. 
Ewart, recognizing that water is a liquid of definite viscosity and that the 
channels through which it moves are small, thereby offering great resistance, has 
endeavored to ascertain the amount of this resistance in definite cases, and the 
possible means by which is generated the force necessary to raise water at the 
required rate.t3 He finds that the flow of water through open vessels is in accord 
with PotsEUILLE’s formula deduced from flow through rigid tubes; hence 
velocity is proportional to the pressure and to the square of the radius of the 
tube, and inversely proportional to the length of tube and viscosity of the liquid. 
The total resistance in erect stems corresponds to a head of water 6 to 33 (for 
shrubs and small trees) or 5 to 7 (for large trees) times the height of the plant. 
Hence, in the tallest trees, the pressure required may be as much as 100 atme® 
pheres. The maximal osmotic suction of leaves in an elm 187 high was 2-3 
12 STEINBRINCK, C. Ueber dynamische Wirkung innere Spannungsdifferen2™ 
etc. Flora 93:127-254. 1904. 
13 Ewart, A. J., The ascent of water in trees. 
B. 198: 41-85. 1905. 
Phil. Trans. Roy. Soc- London 
