78 BOTANICAL GAZETTE [yuLY 
BROWN reports no determinations of osmotic pressure, but finds that if closed 
leaves of Dionaea are killed, before the extension of the cells has become fixed, 
and passed through alcohol to xylene, the leaves reopen, and close again when 
passed back through alcohol to water. He concludes that the increase in size 
of the cells is due to increased osmotic pressure. He believes there is no permea- 
bility change, and thinks changes in the elasticity of the cell walls improbable. 
It is interesting if, in fact, the mechanics of these two responses, so similar in 
many respects, are so widely different in another. 
Geotropic bending of growing organs is similar in many respects to the 
movements studied. Its comparative slowness should make it somewhat easier 
to follow, and the results might furnish valuable suggestions as to the mechanics 
of these more rapid movements. SMALL?’ has found differences in permeability 
in the two flanks of Vicia Faba, roots bending geotropically—THomas 
PHILLIPS. 
Soil moisture studies.—The extensive investigations of Briccs and 
SHANTZ have shown the importance of the moisture equivalent as a constant 
that will measure the physical properties of soils. Two recent studies deal with 
certain phases of the same phenomena. The first* shows that while the addi- 
tion of various salts does not materially change the moisture equivalent of the 
soil under investigation, if the same salts are washed from the soil with water 
it then seems to ss a new and peculiar set of physical properties and its 
moisture equivalent is markedly increased. This increase varies from 2 to 40 
per cent, and is taken to mean that the washing out of the salt has increased 
the interior surface of the soil. 
The second article, by SmrrH, reports the investigation of the relationship 
between the results of mechanical analysis and the moisture equivalent. He 
concludes that there is at present no formula that gives more than a rough 
approximation of this relationship, and hence that the moisture equivalent 
cannot be indirectly determined by mechanical analysis with any degree of 
accuracy.—GEo. D. FULLER 
Soil aeration and root growth.—Roots of various plants appear, according 
to the results of CANNON and FREE,® to respond quite differently to variations 
in the composition of the soil atmosphere, and this difference in response seems 
*7 SMALL, JAMES, Geotropism and the Weber-Fechner law. Ann. Botany 31:3137 
314. 1917. 
* Suarp, L. T., and Waynick, D. D., The moisture equivalent determinations of 
salt-treated soils and their relation to changes in the interior surfaces. Soil Sci. 4:463- 
» SitH, ALFRED, Relation of the mechanical analysis to the moisture equivalent 
of soils. Soil Sci. 4:471-476. 1917. 
%° Cannon, W. A., and Free, E. E., The ecological significance of soil aeration. 
Science, N.S. 45:178-180. 1917. 
