Feb. 3 ,1923 Use of Alternating Temperatures in Seed Germination 311 
Effect of various lengths of time at the warmer temperature of an alternation 
Six lots of seed were germinated with temperature alternations of 
25 0 to 40° C. and 30° to 45 0 C., in which the seeds were in the warmer 
chamber two, four, six, and eight hours each day. Figure 9 shows the 
average germination. The numerals in the position of exponents to the 
temperature conditions at the top of the figure indicate the number of 
hours at the warmer temperatures. This figure illustrates again the 
fact noted in connection with Figure 6, that germination is more rapid 
during the first few days, proceeds at a more nearly uniform rate, con¬ 
tinues for a longer time, and reaches a higher total percentage with the 
alternations 30° to 45 0 than with the alternations 25 0 to 40°. Eight 
hours daily at 45 0 , however, reduced the rapidity of germination in the 
first two days below that with the alternations 25 0 to 40°. The rapidity 
of germination with the alternations 25 0 to 40° increased regularly as 
the length of time in the warmer germinating chambers increased. 
Differences in response of individual lots of seeds to these eight tem¬ 
perature conditions are shown in Figure 10 which gives the percentages 
of germination of three lots of seed in 13 days. 
No. 8604 was a readily germinating lot composed of seed about 10 
months old. The germination of this lot was, within the limits of experi¬ 
mental error, identical under all eight temperature conditions. 
No. 1417 was about 2 years old. It germinated much better with the 
alternations 30° to 45 0 C. than with the alternations 25 0 to 40°, but showed 
little difference according to the length of time in the warmer chamber. 
The lot designated “San Antonio, 1917,” was harvested from wild 
plants near San Antonio, Tex., a few weeks before the tests were made 
and had not after-ripened. In contrast to No. 1417, this lot germinated 
better with the alternations 25 0 to 40° C. than with those 30° to 45°; 
with both sets of alternations the percentage of germination decreased 
with increase in the length of time in the warmer chamber. At the end of 
13 days this lot of seed was still germinating at the rate of about l / 2 per 
cent per day, more rapidly with lie alternations 30° to 45 0 C. than with 
the alternations 25 0 to 40°, so that the germination with the two sets 
of alternations would have become more or less equalized with longer 
germination period. Whether the difference between this lot and No. 1417 
is characteristic of differences between old seed and fresh seed not after- 
ripened is not known. Seed from the same locality as the San Antonio lot, 
collected one year earlier and tested at the same time, germinated better 
with all four of the alternations between 30° and 45 0 C. than with the 
alternations between 25 0 and 40°, in this respect resembling No. 1417. 
Furthermore, it is known that the germination temperatures of some 
seeds change with the progress of after-ripening. At any rate the differ¬ 
ences obtained here illustrate the apparent impossibility of finding any 
single temperature condition which will be the optimum for every indi¬ 
vidual lot of seed, regardless of its peculiarities or its previous history. 
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