REPORT OF THE SECRETARY 7 



of daily solar-constant observations at the three field stations at 

 Montezuma, Table Mountain, and Mount St. Katherine from 1923 

 to 1939, The rest of the text for volume 6 of the Annals of the 

 Observatory was also nearly completed, and the whole is expected 

 to be ready for the printer before January 1942. During preparation 

 of a paper on "An Important Weather Element Hitherto Generally 

 Disregarded," Dr. Abbot noted that the solar variation is several 

 times greater in percentage for blue-violet rays than for total radia- 

 tion. This led him to consider whether the sun's variation might 

 not be more effectively followed by observations limited to the blue- 

 violet region of the spectrum. He finally devised a method of thus 

 restricting the observations, which was introduced near the close 

 of the year at the three field observing stations. There is great 

 hope that the new method will j'-ield more reliable daily indications 

 of the solar variations. Dr. H. Arctowski continued his meteoro- 

 logical investigations relating to the effects of solar variation on 

 atmospheric barometric pressure and temperature and completed a 

 manuscript incorporating the results of this study which Avill be 

 published during the coming year. Daily determinations of the solar 

 constant of radiation were made at the three field stations whenever 

 conditions permitted. A new concrete dwelling house for the 

 observers was erected at the Montezuma station. 



Division of Radiation and Organisms. — The Division continued its 

 program of research on the relation of radiation to various phases of 

 plant growth. In continuing the project dealing with the genesis of 

 chlorophyll and the beginning of photosynthesis, a large amount of 

 information was obtained on the respiration of etiolated barley seed- 

 lings. This material is important because of its bearing upon photo- 

 synthesis as measured by the gaseous exchange method. It appears 

 that conditions of carbon dioxide storage or depletion develop in 

 the plant tissue depending upon the concentration of this gas sur- 

 rounding the plants. In subsequent periods, when the respiration is 

 measured there is an increase or decrease in the rate of CO2 excre- 

 tion (i. e,, in the apparent rate of respiration) until a state of 

 equilibrium with the new environment is attained. Considerable 

 time was spent in improving the performance of the spectrograph 

 used in measuring carbon dioxide for very short periods, and the 

 new features developed have greatly improved the speed-sensitivity 

 and stability of the apparatus. Further study was made of the 

 spectral effectiveness of radiation for the growth inhibition of the 

 oats mesocotyl, and a comparative study was undertaken of some 

 other species of grasses. A paper resulting from experiments in the 

 ultraviolet irradiation of algae showed that algae exposed four times 



