Feb. 3,1923 Use of Alternating Temperatures in Seed Germination 331 
ditions—than those lots which germinate less readily even under the 
most favorable conditions. 
(13) A large percentage of some lots of Johnson grass seed will go 
through at least the first visible stages of germination and some of the 
seeds will develop apparently healthy seedlings at warm constant tem¬ 
peratures (35 0 to 40° C.), but a part of the seedlings are abnormal and 
capable of only slight development at these temperatures while the 
percentages of germination remain below those for favorable alternations 
of temperature. 
(14) With alternations between 25 0 and 40° C. or between 30° and 45 0 
the length of time from two hours to eight hours during which the seeds 
are kept in the warmer chamber has little effect on the percentage of 
germination of fully after-ripened Johnson grass seed but affects the rate 
of germination somewhat more. 
(15) Removal of the scales from Johnson grass caryopses greatly 
increases their germination under relatively unfavorable temperature 
conditions, somewhat increases their germination with the most favorable 
temperature alternations, and considerably accelerates their germination 
in both cases. 
(16) The temperature changes to which the seeds are subjected in any 
given alternation vary with their position within the germinating chamber 
and with the method of testing (whether between or on top of wet 
blotters) and are in no case exactly the same as indicated by a ther¬ 
mometer inserted into the air in the top of the chamber. 
(17) The temperature changes giving best germination results with a 
large number of kinds of seed correspond rather closely with soil tempera¬ 
tures in the field under conditions which induce the most prompt and 
vigorous production of seedlings. A similar correspondence undoubtedly 
exists between the temperature conditions, giving best results with 
Bermuda grass and Johnson grass seed on the one hand and soil tem¬ 
peratures in the warmer localities to which these grasses are native on 
the other hand. 
(18) The results of field tests suggest the use of an alternation between 
about 18° and about 32 0 C. for the germination of a large number of 
kinds of seed; an alternation covering a lower temperature range than 
20 0 to 30° with onion seed; and an alternation covering a considerably 
higher temperature range with seeds of the cucurbits. Without experi¬ 
mental evidence, however, it is impossible to say whether or not any of 
these alternations in the cases indicated would have any advantage over 
an alternation between 20° and 30°. 
LITERATURE CITED 
(1) Brown, E. 
1902. GERMINATION OP KENTUCKY BLUE GRASS. In U. S. Dept. Agr. Off. 
Exp. Sta. Bui. 115, p. 105-110. 
(2) Burchard, O. 
1892. ueber die temperatur bei keimversuchen. In Oesterr. Landw. 
Wochnbl., Jahrg. 18, p. 274-275. 
(3) CiEsear Adolf. 
1883. UNTERSUCHUNGEN UBER DEN ElNFEUSS DES UCHTES AUP DIE KEIMUNG 
DER samen. In Forsch. Geb. Agrikultur-physik, Bd. 6, p. 270-295. 
Bibliographical footnotes. 
(4) Dorph-PetersEn, Knud. 
[1921]. STATSFR 0 KONTROEEEN (DANSK FR 0 KONTROE) 1871-1896-1921. XVi, 160 
p., 23 fig. Kobenhavn. 
(5) Eidam. 
[1883]. UEBER DEN ElNFEUSS WECHSEENDER FEUCHTIGKEIT UND TEMPERATUR 
AUF DIE KEIMUNG DER GRASS AMEN UND DER RUNKEEKNAUEE. In Ber. 
Bot. Sect. Schles. Gesell., 1883, p. 232-239. 
