260 BOTANICAL GAZETTE [APRIL 
These data offer no evidence of a reciprocal relation between 
heat and light as suggested by LEHMANN and OTTENWALDER, not 
even in the case of seeds of Verbascum Thapsus, nor have any of 
the various tests indicated this reciprocal relation in the seeds. 
Indeed, in each kind of Seed under investigation the optimum 
temperature for germination in light is very close to that for 
germination in darkness. In germination in darkness the results 
show rather definite minimum and maximum as well as optimum 
temperatures. It is especially noteworthy that high temperature 
and darkness did not induce germination of Verbascum Thapsus 
seeds, as claimed by OTTENWALDER (40). No specific experiments 
were performed to determine the effect of light intensity on germina- 
tion, although early in this investigation it became a very familiar 
fact that very little illumination would induce germination. Good 
germination in darkness was frequently the occasion for repetition 
of an experiment, only to find that germination had been induced 
by leaks in the light screens. A comparison of table VI with data 
given elsewhere indicates that highest germination of light-sensitive 
seeds does not occur at constant temperature, but at temperatures 
fluctuating between 20 and 27°C. 
Effects of alternation of temperature, light, and darkness 
As long ago as 1882 NoBBE (39) and his students used alternating 
temperatures to promote germination, and in 1884 LIEBENBERG (35) 
referred light effects to variations of temperature in the germination 
of seeds of Poa pratensis. As recently as 1911 PICKHOLTZ (42) 
referred the action of light in promoting germination to the 
effects of heat rays. In an attempt to distinguish the effects of 
light from those of temperature the following experiments were 
performed. Seeds of each kind were counted into Petri dishes with 
filter paper wetted with distilled water as substratum. One lot of 
cultures was placed in darkness on February 9 at 40° C., where it 
remained for 17 days. Another lot of cultures was placed in dark- 
ness at temperatures ranging from o to 12°C. for17 days. Another 
lot was kept in darkness and subjected alternately to high tempera- 
ture (40°C.) and low temperature (o-12°C.) for nearly equal 
periods throughout the 17 days. The low temperature and the 
