1922] CURRENT LITERATURE 119g 
In this and in a previous paper,® PARKER holds that the freezing point 
depression for the moisture equivalent and probably also for the wilting 
coefficient is practically a constant for all soils. This may be taken as addi- 
tional evidence that the moisture equivalent and wilting coefficient are within 
very considerable limits constants for all soils——Gro. D. FULLER. 
Physicochemical problems relating to soil.—Under this title? the Faraday 
Society has brought together in book form the papers ‘presented before the 
Society during the general discussion of this topic at its meeting in London 
on May 31, 1921. The discussion is divided into five sections, and was 
planned to form a rather complete survey of the subject. The first section 
is general in nature, and consists of a survey of the whole field by RussELL, 
and a discussion of the physical properties of soils in relation to survey work 
by Roxsinson. The second section deals with the problems of soil moisture, 
with papers by KEEN, OpEN, HOAGLAND, SHULL, and Hackett. The third 
section considers the organic constituents of the soil, with papers by Pace, 
OpEN, and Satispury. The last two sections are concerned with colloidal 
properties, the adsorption phenomena of section four being discussed by 
FiscHER, CROWTHER, and Morrison. The final section deals with the 
dispersity, flocculation, and plasticity of clays by ODEN, ComMBER, and MELLor. 
The discussion as a whole forms an important addition to soil literature, 
and one is impressed by the usefulness of such symposia as the Faraday Society 
has organized from time to time. The custom of holding such general discus- 
sions devoted to an entire survey of some field of investigation is one that might 
well be established among scientific societies in this country to replace the 
less valuable type of symposium now in vogue here.—C. A. SHULL. 
Photosynthesis control in forest plants.—In investigating the conditions 
affecting photosynthesis in forest undergrowth, LUNDEGARDH’ using a new 
form of assimilation-chamber, found that with variations of carbon dioxide 
concentration and low light intensities both the light and the carbon dioxide 
supply are controlling factors. The advantages from a supply of carbon 
dioxide above normal appear most strongly in low intensities of light. For 
Oxalis acetosella at 0.025 of sunlight, and for Viola tricolor at 0.25, an approxi- 
mately direct proportionality was obtained between the carbon dioxide concen- 
tration and the intensity of photosynthesis. In the forest, on account of the 
production of the CO, by the ground, the air (especially that nearest the 
ground) becomes rich, the CO, content often rising to more than twice normal. 
This increase, least over sandy soil and greatest over the humus of beech woods, 
ARKER, F. W., Methods of ee the concentration and composition of 
the soil solution. Soil Science 12: Seedes 32. 
7 Physicock I ting to the soil. Trans. Faraday Soc. 17: 217-368. 
1922, 
* LUNDEGARDH, HENDRIK, Ecological studies in the assimilation of certain forest 
plants and shore plants. Svensk, Bot. Tidsk. 15:46-95. figs. 9. 1921 
