Physiologie. 581 



method et" investigation and the types of soil are totally ditferent 

 in the two cases; both deduce a linear equation to cxpress the 

 equilibrium under stated conditions, and both point to the soil 

 moisture under such conditions being an adequatc and simple index 

 of the soil. Briggs and McLane's "moisture equivalent" is Ihe 

 percentage of moisture a soil can retain when subjected to a cen- 

 trifugal force about 3000 times that of gravity, and the magnitude 

 of this equivalent for any soil depends almost wholly and equally 

 upon the clay and humus present. 



In discussing the broader aspect of the problems involved in 

 the investigation of soil moisture in relation to the plant association, 

 the author^points out that if the coefficient of soil humidity is to be 

 of Service in ecology a thorough study of definite habitats must be 

 made, and he indicates the lines on which this can be prosecuted 

 with advantage. The mean value of this coefficient is the most 

 important constant to be ascertained for every association whose 

 distribution and existence are determined by soil moisture; but the 

 coefficient for every such association will vary considerably from 

 its mean value, and there will be maximal and minimal values, 

 besides a supra-maximal and a sub-minimal value determined not 

 by competition but by the physiological relations of the root-systems 

 with the soil-water: when these values are reached and maintained 

 the association can no longer continue to exist. F. Cavers, 



Cpump, W. B., Notes on Water-content and the Wilting- 

 point. (Jour. of Ecology, I. nO. 2. p. 96—100. 1913.) 

 The paper gives a short summary of the author's conclusions 

 in the case of water-content of acidic peats. It is shown that a 

 complicated series of peats from the Pennines (England) may be 

 reduced to a homologous series, each homologue, corresponding to 

 a recognised plant-association, being distinguished by its water and 

 humus Contents. Results are also given on the wilting of moorland 

 plants, and this leads to a criticism of the investigations of L. T. 

 Briggs and H. L. Shantz. W. G. Smith. 



Fpitsch, F. E. and E. J. Salisbupy. Some simple Physiolo- 

 gical Demonstrations. (New Phvtologist. XII. p. 191 — 194. 

 1 textfig. 1918.) 



The authors describe, with illustrations, a number of simple 

 but effective methods of physiological demonstration including the 

 foUowing. 1) An artificial Stoma: stems of herbaceous plants are 

 used instead of rubber tubing to represent the two guard-cells; the 

 two stems are tied at each end and placed successivelj^ in salt 

 Solution and in water, to show the "closing" and "opening" move- 

 ments respectively. 2) Continuity of the aerating System: the action 

 of an air-pump is replaced by the condensation of steam and con- 

 sequent reduced pressure in a fiask half-filled with water which 

 is then boiled. 3) Recovery of a flaccid shoot; the same appa- 

 ratus is used, the suction causing rapid flow of water through 

 the shoot. 4) Rate of flow of water through the wood: the same 

 apparatus is used for comparison of rates of flow in a Dicot3iedon 

 and a Coniferous stem, the two stems being passed through holes 

 in the stopper of the flask. 5) Demonstration of water-pores: the 



