340 CARNEGIE INSTITUTION OF WASHINGTON. 



the sahuaro enlarged during the day and diminished during the night. This 

 was thought to be related to the stomatal movement, and several series were 

 made to determine the latter during the 24 hours, together with measure- 

 ments of transpiration. A close correspondence was disclosed between water- 

 loss and stomatal movement, and a causal connection between the former 

 and changes in trunk diameter. The stomata of Cereus were found to open 

 gradually through the night after 6 p. m. and to close before noon of the next 

 day, while the rate of transpiration increased and decreased with the degree 

 of stomatal opening. Hence, it was greatest during the night and had dis- 

 appeared by the middle of the day. The trunk regularly expanded when 

 the stomata were closed and transpiration prevented, and contracted when 

 the latter again became appreciable. Expansion of the trunk occurred during 

 the day at a time when other plants were dying or shedding their leaves for 

 lack of water, indicating that the echard is much lower for this species. 



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



Further work on the dissolved gases in bog-water indicates that, while the 

 oxygen-content of the lower levels may be reduced beyond the sensibility of 

 the Winkler method, the carbon dioxid and the acidity vary in proportion to 

 the photosynthetic activity of the algal flora. The bogs at high altitudes 

 in the Pike's Peak region are anaerobic during the winter, when the ice prevents 

 active gas interchange with the air, and at such times are often charged with 

 H2S. During the summer the surface water is in approximate gaseous equilib- 

 rium with the air, but anaerobic conditions usually persist at a depth of a 

 meter or more. In the open pools, where light intensities permit the growth of 

 algae, anaerobic conditions prevail only well below the algal zone. 



The field study of soil-air and of the acidity and gases of the soil-solution 

 has been extended to include mesophytic and xerophytic habitats. A 

 complete portable outfit for the field has been developed for measuring the 

 volume of soil-air, as well as its composition. The results so far obtained 

 indicate that the accepted estimates of the amount of air in various soils are 

 too high. Measurements are also being made of the amount and composition 

 of the air in the roots and stems of plants, especially amphibious ones, and the 

 earlier experiments on aerotropism and the behavior of roots under anaerobic 

 conditions have been resumed and extended. 



Photometers and Photometric Methods, by F. E. Clements and J. V. G. Loftfield. 



The simple photometer and the selagraph or recording photometer 

 developed more than 20 years ago have been improved and modified to form 

 a series of instruments which now includes the stop-watch photometer, water 

 photometer, selagraph, water selagraph, and a portable electric spectro- 

 photometer. The simple photometer has been largely replaced by the stop- 

 watch one, which is much more accurate and convenient to use, and the water 

 selagraph is designed to replace the water photometer, which must be turned 

 for each exposure and hence is hard to operate at considerable depths. 



While the solio paper used in the photometers and the azo paper employed 

 in the selagraphs have given dependable results in a wide variety of investi- 

 gations, their value is now being tested by means of bromide papers sensitized 

 with sodium nitrate and by this with erythrosin, according to formulae kindly 

 furnished by Dr. C. E. K. Mees, of the Eastman Laboratories. In addi- 

 tion, the Ridgway chemical photometer is being tried out in the expectation 



