368 BOTANICAL GAZETTE [MAY 
condition to which the plants were exposed was the air of the day- 
time on the one hand, and that of the night on the other. Are 
there then any differences in the atmospheric air during day and 
night which might account for this remarkable variation in the 
respiratory activity? The first thing to suggest itself is the possible 
influence of the sunlight on the atmosphere. 
The intensity of the violet and ultra-violet rays of the sunlight, 
as measured at the Desert Laboratory during 18 months, compared 
with the values generally given for atmospheric ionization, showed 
a remarkable similarity. Drmprr’ and others® have reported the 
same fact from observations in other localities. Physicists are 
not agreed as to the exact relation between sunlight and atmospheric 
ionization,’ nor is a discussion of this subject necessary for the pres- 
ent purpose. Suffice it to note that according to the observations 
of Etster and Griret, A. GOCKEL, VON SCHWEIDLER, and others, 
atmospheric ionization exhibits a main maximum about noon, a 
secondary maximum a little before sunrise, with minima after sun- 
set and before sunrise. These values are subject to certain varia- 
tions, since the ionization is affected by other meteorological factors, 
as is mentioned below. 
Im general, then, the highest respiratory activity takes place 
during the period of increased ionization. If the respiratory 
activity and atmospheric ionization are in any way related, the 
artifical deionization of the air drawn over the plants should have 
a marked effect on their respiratory activity under the present 
experimental conditions. 
7 Demper, H., Uber die ionisierende Wirkung des ultravioletten Sonnenlichts. 
Physik. Selina: 132207-212. I 
8 KAEHLER, K. ORT: Leipzig. 1913 (p. 69). 
9 Lenar, P., and Ramsaver, C., Uber die Wirkung Ultravioletten Lichtes auf 
Gase unter besonderer a ns der Vorginge in der Erdatmosphaere. 
Metrol. Zeitzchr. 29:150. “2 
Lenarp, P., Uber die Wika de des Uiteavioletten Lichtes auf Gasférmige Kérper. 
Ann. Phys. 1: 486. 1900; 3:298. 1 
Tuomson, J. J., Pecdartins we electricity through gases. Cambridge. 19%3 
2 
. ney J., and Gerret, H., Die Existenz elektrischer Ionen in der Atmosphare. 
Jour. Terr. Magnetism and Atmos. Elect. 4:213. 1899. 
Stark, J., Die Elektrizitat in Gasen. Leipzig. 1902. 
