Feb. 3,1923 Use of A Iternating Temperatures in Seed Germination 299 
separated from each other. 
But the differences ob¬ 
served in the early days 
of the test were evened 
up toward the end, ex¬ 
cept with the warm tem¬ 
perature alternation 30° 
to 35 0 C. and at 35 0 
constant. 
2 . SEEDS REQUIRING TEM¬ 
PERATURE alterna¬ 
tions 
Seeds of redtop, orchard 
grass, Kentucky bluegrass, 
Bermuda grass, parsnip, 
celery, and Johnson grass 
required an alternation of 
temperatures for best ger¬ 
mination. Of these, red- 
top comes nearest to 
being a constant-tempera¬ 
ture germinator and Ber¬ 
muda grass stands at the 
other end of the series. 
REDTOP 
Figure 2 shows the av¬ 
erage percentages and 
rates of germination of 
three samples of redtop 
seed. Alternations be¬ 
tween extremes io° C. 
apart (20° to 30° and 25 0 
to 35 0 ) gave the highest 
results, with 5 0 and 15 0 
alternations only slightly 
lower but still somewhat 
ahead of the constant tem¬ 
peratures. As with the 
constant-temperature ger- 
minators, so here in the 
tests with redtop, constant 
temperatures below or 
very much above the 
optimum and alternations 
15 0 wide (20° to 35 0 ) re¬ 
tarded germination in the 
early days of the. test. 
At the end of the first 
three days the^ influence 
Fig. 2.—Average rates and percentages of germination of three 
lots of redtop seed under seven temperature conditions. 
