ECOLOGY. 305 



the epidermal cells just before maximum opening occurred. After this time, 

 the concentrations within the two sets of cells distinctly approached each 

 other as a rule, although the stomata might remain completely open. As the 

 stomata began to close, the concentration of the guard-cells dropped and 

 became less than that of the epidermal cells for a time. After closure was 

 completed, the two concentrations again approached and soon became identi- 

 cal, equilibrium being established. The average concentration of the epi- 

 dermal-cell sap at the three stations varied considerably. Work is also in 

 process to determine the changes in the sap of the chlorenchyma-cells during 

 a 24-hour period, as well as the rate of permeability to the hexoses and sucrose. 

 An attempt was made to correlate conduction, as measured by a modifica- 

 tion of Farmer's method, with transpiration and leaf area. Previous work 

 had shown that no definite relation existed between stem diameter and con- 

 duction, but a number of interesting relations were found in regard to the 

 region at which the stem was selected. Such a relation seemed also to exist 

 between the number of leaves and the amount of conduction. It was often 

 found that it made but little difference in the rate whether the entire stem 

 was used, the water then escaping from the cut ends of the petioles, or a short 

 section from the base. Thus, the basal portion of the stem seemed to deter- 

 mine the rate of conduction. This, however, varied in most cases with the 

 number of active or mature leaves, as well as with the habitat from which 

 it had been taken. The stems of the sunflowers from the three factor stations 

 were used in the determination of the ratio between leaf area and the rate of 

 conduction. Great variation occurred at all times, and this may possibly 

 be attributed to experimental difficulties in using soft, weak stems, but in 

 consequence the results are not entirely conclusive. Extreme variation was 

 exceptional, however, and in most instances the results corresponded closely. 

 The sun-station plants (the extremes not included) gave a ratio of 0.47 c.c. 

 (±.005) per hour per square decimeter of leaf, partial-shade station plants 

 0.87 c.c. (±.02), and shade-station plants 0.43 c.c. (±.005). The differences 

 found at the various stations are not necessarily explainable by the average 

 transpiration rates but apparently by the extreme rates of transpiration. 



Studies in Aeration, by F. E. Clements and G. W. Goldsmith. 



The apparatus for the determination of the quantity and quality of soil-air 

 has been improved so as to simplify field manipulation and increase the 

 accuracy of the determinations. Readings made during the dry winter 

 season on the prairies near Colorado Springs indicate that moisture rather than 

 temperature is the factor limiting the activities of soil micro-organisms in this 

 region. During prolonged diy periods the air-content of the soil approaches 

 atmospheric air in composition, but when these droughts are broken by a 

 rain the free oxygen of the soil-air is rapidly reduced and the carbon dioxid 

 increased as far as the moisture penetrates. The deeper layers of the soil, 

 which are uniformly dry throughout the season in this region, maintain a 

 winter atmosphere similar to the free air. Since root activity is presumably 

 slight during the winter, atmospheric changes following the addition of 

 moisture are probably due to the activities of the micro-fauna and flora of the 

 soil. The dominant plants of this region must therefore be able to maintain 

 root absorption in reduced oxygen pressures and increased carbon-dioxid 

 tensions, and this capacity may be of much importance in the growth and com- 

 petition relations of the dominants and subdominants. 



