ECOLOGY. 393 



lected for histological study in the laboratory. A considerable num- 

 ber of poly demies has been included, and factor readings of the various 

 habitats are available for these as well as for other species of the 

 different communities. 



It is thought that the transpiring power, as determined by the 

 cobalt-paper method, may furnish a means of measuring habitat 

 differentiation. It if prove possible to determine the relative degree 

 of xerophytism of the dominants and subdominants of each com- 

 munity, this method may assist materially in the classification of the 

 habitats and stages in a given succession as well as in that of climax 

 communities. It is evident that it can only serve as a short cut to the 

 measurement of transpiration, and that its value must depend upon a 

 close correlation with the latter as determined by actual field studies. 



The Role of Soil-air in Hydrophytic Habitats, by F. E. Clements and G. W. 



Goldsmith. 



In preparation for a comprehensive study of the significance of the 

 air-content of the soil, a fairly complete summary of existing knowl- 

 edge has been given in "Aeration and Air-content" (Carnegie Inst. 

 Wash. Pub. 315, 1921). In resuming actual investigation, attention 

 has been chiefly directed at the outset to swamps and bogs and to wet 

 soils generally, as these offer the most striking effects. Ultimately, 

 it is planned to deal with the soil-air of cultivated as well as natural soils, 

 and to devote especial attention to the relation of soil-air to acidity 

 and to the toxins of both bogs and agricultural soils. 



The oxygen-conten and the COa-content, the acidity, and their 

 effects upon the growth and transpiration of various plants, as well as 

 the animal life, have been studied in various conditions in the cypress 

 and coastal swamps of southern Louisiana, and in the plains swamps 

 and alpine bogs about Pike's Peak. A compact but complete portable 

 equipment for gas analysis has been constructed, so that all the de- 

 terminations are made in the field. Winkler's method has been 

 employed for the estimation of oxygen, and Seyler's modification 

 of Pettenkoffer's method for determining the carbon dioxid. The 

 acidity of samples has been determined by both colorimetric and 

 electrometric means, but the latter has been found to yield much 

 greater accuracy. Determinations are made either in the field or 

 laboratory by the use of a Leeds and Northrup portable potentiometer 

 and a Bailey hydrogen electrode. Plankton catches are made with 

 each set of samples taken, in order to measure the complete biotic 

 response. 



In the Louisiana swamps there is usually an alkaline reserve, so 

 that the H-ion concentration runs about pH 8, even in the poorly 

 aerated lower layers. Nevertheless, characteristic swamp plants, as 

 well as sunflowers, show a great reduction in the transpiration rate 



