252 BOTANICAL GAZETTE [APRIL 
and OTTENWALDER (36) experimented with Epilobium hirsutum 
and other seeds and showed that acid solutions and proteolytic 
enzymes can be substituted for light. They referred the light 
effect to activation of enzymes, but did little to prove their 
hypothesis. PicKHoLrz (42) connected light effects and tempera- 
ture variations, and concluded that the influence of direct sunlight 
was mainly due to the heat rays which raised the temperature. 
Alternating temperatures helped the germination at different stages 
of maturity. 
In 1912 a number of workers reported on the problem of light 
germination. Baar (1) investigated seeds of several Amarantaceae 
and found that most seeds of this family (Amaranthus, Celosia, and 
Blitum) have an aversion to light. He considered the age of seeds 
generally important for the occurrence and intensity of the light 
effect, and also related the light effect to substratum and temper- 
ature variations. BECKER (2) brought forward a long list of 
examples of the light effect on germination of seeds. Haack (18) 
in his work on the Scotch pines demonstrated the influence of 
heat, and reported that temperature variations act as a stimulus to 
light-sensitive seeds, and that blue light is more favorable to germi- 
nation than darkness. Simon (47) reported that the salts of iron 
hindered germination of seeds in darkness, but increased it in light. 
GASSNER (12) first reported on the germination of seeds of Chloris 
ciliata in 1910. He found three factors which may be substituted 
for light, namely, increased oxygen supply, after-ripening, and 
high temperature. He claimed that light offsets the effect of the 
limiting factor, and showed that the chaff of Chloris ciliata prevents 
easy germination. His later work (14, 15) took up the action of 
chemicals. He considered the latent influence of light as related 
to seed bed, temperature, and after-ripening, the influence of light 
on germination, the influence of desiccation, and the relations 
between light and media favoring or hindering germination. From 
a tabulation of tests with seeds of different families he concluded 
that in these cases nitrogen, variously combined in the media, 
shows the same favorable action as light, but he included contradic- 
tory results. He considered the favorable effect of Knop’s nutrient 
solution as due only to the nitrates present. He reported the seeds 
