3°8 
Journal of Agricultural Research voi. xxiii, no. s 
With the extremely warm temperature alternation, 35° to 50° C., the 
percentage of germination was low and the majority of the seedlings 
failed to make normal growth. 
Concurrent germination tests of the six lots of seeds whose germina¬ 
tion is represented in Figure 6 were made also at 15 0 , 45°, and 50° C. 
and with the temperature alternation 40° to 55 °. Less than 1 per cent 
germinated at 15 0 C., and these made but little growth. At the higher 
temperatures none germinated in six days. These seeds were then 
given the temperature alternation 25 0 to 40° C. for seven days, followed 
by viability tests 4 with the alternation 30° to 45 0 C. Viability tests 
showed that all but a fraction of 1 per cent had been killed by six days r 
exposure to 50° C. or the alternation 40° to 55°. A temperature of 45 0 C. 
for six days had killed more than half of the seeds of some of the lots, 
but only a few of the seeds of other lots. The seedlings produced were 
relatively weak. 
Differences between individual lots of seed 
Different lots of Johnson grass seed vary greatly in the readiness 
with which they germinate, and it has been found that poorly germi¬ 
nating lots are more sensitive to temperature conditions than lots which 
germinate more readily. This is illustrated in Figure 7 which repre¬ 
sents the total germination in 16 days of two of the lots included in the 
averages for Figure 6. No. 8599 was grown at Arlington Farm, Va., 
and gave a fairly ready germination. The San Antonio lot was col¬ 
lected from wild plants near San Antonio, Tex., and gave poor germina¬ 
tion. While the general shape of the two graphs in Figure 7 is the 
same, favorable alternations and especially the best alternation, 30° to 
45 0 C. showed greater advantage over constant temperatures and less 
favorable alternations in the case of the San Antonio lot than in the 
case of the other lot. Viability tests 5 showed 94 per cent of the San 
Antonio lot and 95 per cent of the other lot to be alive and capable of 
producing vigorous seedlings. 
Effect of removal of the scales 
The effect of removal of the scales (glumes, or hulls) upon the germina¬ 
tion of Johnson grass caryopses has already been pointed out (u). The 
effect is illustrated in Figure 8, which shows the average percentage of 
germination in 13 days of two lots of seed intact and with the scales 
removed. The increase in germination as a result of removing the scales 
is especially noteworthy at the warm constant temperatures 30°, 35°, 
and 40° C. 
In the preceeding section it was shown that readily germinating lots 
were less sensitive to temperature conditions than lots which germinated 
poorly. Increasing the readiness with which a given lot germinates 
and at the same time diminishing its sensitiveness to temperature con¬ 
ditions by removal of the scales merely constitutes a special case of the 
previous rule. The rapidity of germination also is greatly increased by 
removal of the scales. 
4 See footnote on page 307. 
* See footnote on page 307. 
