Feb. 3, i 9 2 3 Use of Alternating Temperatures in Seed Germination 297 
In these germination tests it was not possible with the equipment 
available to control the temperatures absolutely, but except for 15 0 and 
20 0 C. the fluctuations were very slight. Even with these lower tempera¬ 
tures the control was sufficiently accurate to give reasonably reliable 
results, as will appear later. 
Seeds of celery and redtop were tested on top of four thicknesses of 
moistened blotting paper. Kentucky bluegrass and Bermuda grass 
seed were tested with the Jacobson apparatus (4, p. 33) . The other kinds 
were tested between moistened blotting papers, two thicknesses below 
and two above. 
The following year a study was made of the actual progress of tempera¬ 
ture changes in the interior of the germinating chambers in a variety of 
temperature alternations, and these temperature changes, with the 
resulting effects upon the germination of a number of kinds of seeds, were 
compared with data obtained from field experiments. 
About two years later a number of kinds of flower seeds were tested at 
very accurately maintained constant temperature from 15 0 to 30° C. 
with a large number of temperature alternations. Some kinds were 
tested also in an ice box. The kinds studied were balsam {Impatiens 
balsamina L.), California poppy ( Eschscholtzia californica Cham.), candy¬ 
tuft ( Iberis amara L-)> cosmos {Cosmos bipinnatus Cav.), belvedere 
{Kochia scoparia (L.) Schrad.), larkspur {Delphinium ajacis L.), mari¬ 
gold {Calendtda officinalis L.), mignonette {Reseda odorata L.), nastur¬ 
tium {Tropaeolum majus L. and T. minus L.)> pansy {Viola tricolor L.), 
petunia {Petunia hybrida Hort.), Chinese pink {Dianthus chinensis L.), 
poppy {Papaver spp.), portulaca {Portulaca grandiflora spelndens Hort.), 
snapdragon {Antirrhinum majus L.), sweet pea {Lathyrus odoratus L.), 
and zinnia {Zinnia elegans Jacq.). The larger seeds were tested between 
wet blotters or wet canton flannel and the smaller ones on top of wet 
blotters. 
More recently a careful study was made of the germination of Johnson 
grass seed {Holcus halepensis L-) under accurately controlled temperature 
conditions, moistened blotting paper disks in 100-mm. Petri dishes being 
used as a germinating bed. 
In the germination tests of each series duplicates of 100 or 200 seeds 
each were used. The seeds used were fully after-ripened except as 
indicated later in certain tests of Johnson grass seed. The tests whose 
results are presented in this paper are typical examples of a large number 
of tests of the same kinds of seed. 
The results of the first and third series of tests will be presented 
briefly and then the results of the tests of Johnson grass seed will be 
given more in detail, reserving the study of the alternations and com¬ 
parison with field data until last. On account of the nature and com¬ 
plexity of the data dealt with, the results can in general be presented to 
best advantage in graphic rather than in tabular form. 
RESULTS OF THE EXPERIMENTS 
I. SEEDS GERMINATING AT CONSTANT TEMPERATURES 
Seeds of timothy, awnless brome grass, both species of rye grass, 
meadow fescue, carrot, and parsley and all of the flower seeds ger¬ 
minate nearly or quite as rapidly and completely at favorable constant 
temperatures as with any alternation of temperatures. The most 
