JOURNAL OP AfflETORAL RESEARCH 
Vou. XXIII. Washington, D. C., February 3, 1923. No. 5. 
USE OF alternating temperatures IN THE 
GERMINATION OF SEEDS 1 
By George T. Harrington 
Formerly Scientific Assistant , Seed-Testing Laboratories , United States Department of 
Agriculture 
INTRODUCTION 
The helpful use of daily alternations of temperatures in the germina¬ 
tion of certain seeds grew out of observed differences in germination in 
light as compared with that in darkness, and the resulting controversy 
as to whether the favoring effect of light was due to the heat rays or was 
photochemical in nature. 
Cieslar (5) 2 in 1883 secured better germination of Poa nemoralis in 
yellow (therefore warm) light than in white light, although violet (there¬ 
fore cold) light gave no better germination than was secured in darkness. 
Pickholz (79), working with Poa pratenis, later reported similar results 
which indicated that the heat rays were more effective in germination 
than the light rays. While this conclusion has not proved to be true 
with all light-sensitive seeds, it has with some kinds; and the investiga¬ 
tions which followed Cieslar’s work led to the definite policy of germi¬ 
nating many kinds of seeds with a regular daily alternation of tempera¬ 
ture. Usually about 20° C. has been used as the lower temperature and 
about 30° as the higher temperature, the higher temperature being main¬ 
tained for from four to eight hours each day. Many other alternations 
have been used experimentally with good results. 
The year following Cieslar's publication Von Liebenberg ( 16 ) showed 
that Poa pratensis germinated better when kept at 20° C. for 19 hours 
and at 28° for five hours of each day than at either 20° or 28°, constantly 
maintained, and that this alternation of temperatures took the place of 
exposure of the seed to light. Since then others (/, 6, 7, 8 t 9, jz, 75, 
77, i8 y 79, 20, 21) have shown a favorable effect of temperature alterna¬ 
tions upon the germination of many kinds of seeds. Usually a daily 
alternation has been used. Heinrich (13 ), however, showed that a very 
beneficial effect was produced in some cases by a definite temperature 
change once in five days. Lehman (75) argued that a similar favorable 
effect was produced by temperature changes without definite or daily 
alternations, and Gassner (6) showed that only a few hours at a low 
temperature followed by a single change to a higher temperature induced 
maximal germination of seeds of Paspalum dilitatum , which would not 
germinate well without previous exposure to the low temperature. 
1 Accepted for publication May io, 1922. 
Reference is made by number (italic) to “ Literature cited,” p. 331-332. 
Journal of Agricultural Research, 
Washington, D. C. 
aay 
Vol. XXIII, No. s 
February 3, 1923 
Key No. G-274 
25621—23-1 
(295) 
