REPORT OF THE SECRETARY "15 
In August 1945 Dr. Abbot spent several weeks at Mount Wilson, 
Calif., testing his new radiometer and developing plans for improved 
apparatus for measuring the energy spectra of stars. 
(2) DIVISION OF RADIATION AND ORGANISMS 
(Report prepared by Dr. Harl 8S. Johnston, Assistant Director of the Division) 
Project 1. Photosynthesis—For the accurate determination of 
carbon dioxide absorbed by green plants in the process of photo- 
synthesis it is necessary to correct for the amount of carbon dioxide 
eliminated in respiration. Before many of the fundamental prob- 
lems arising in this study can be solved it is absolutely necessary to 
improve the accuracy of the apparatus designed for the measure- 
ments of minute changes in the concentration of carbon dioxide sur- 
rounding the plant. During the past year much time has been given 
to this work and many experiments carried out. Respiration experi- 
ments have been run with barley seedlings, and small animals such 
as the cockroach, cricket, and grasshopper. A most interesting and 
unexplained respiration rhythm has been discovered in the cockroach. 
However, this phenomenon as well as an apparent water-vapor effect 
cannot be fully explained until more work is completed on this delicate 
and highly sensitive apparatus. 
Project 2. Plant growth—tThe study of plant growth under con- 
trolled artificial conditions of mineral nutrition, illumination, tem- 
perature, and humidity has been continued. The experiments carried 
out on wave-length balance indicated a need for improvement in the 
technique used. Further work along this line is being pursued. 
Most of the work under this general project has centered around 
the problem of the role of the environment in the growth processes of 
cereal seedlings. The effects of radiation, which constitute the pri- 
mary problem, have been found to depend upon other environmental 
factors, such as temperature, water supply, humidity, and chemical 
composition of substrate so that it has become necessary to evaluate 
the importance of these. Some of the observations and tentative 
conclusions from these as yet incomplete experiments are listed: 
a. Development of seedling as a whole.—In the growth processes 
of grass seedlings a sharp distinction must be made between the rate 
of growth and the ultimate amount of growth. These two properties 
appear to be antagonistic in the sense that the slower the rate of 
development of a given organ, the longer does growth continue and 
the greater is the final size attained. 
The rate of water absorption appears to be a determining factor in 
controlling the growth processes; the effects of certain other environ- 
