43 
that up to that time it had not been proven whether the germination 
of the seeds was affected by light or by humidity. His own experi- 
ments convinced him that the latter was more important. 
Sénébier (1800) made additional experiments on peas and beans, 
sowing them in sponges, which were kept equally moist, all inclosed 
mabe! glass covers, so that no evaporation could take place. Some 
were exposed to sunlight and some were kept in the dark, but those 
which were in the dark germinated much sooner than those in the 
light. But in such experiments as these the sources of error are 
numerous, and the fact that there was no renewal of the air under 
these covers was especially unfavorable to germination. In fact, 
Leclere (1875) has shown that under the influence of mercurial 
vapor, as it existed in Sénébier’s experiments, a large portion of seeds 
are killed, so that with our present knowledge we can not accept 
Sénébier’s conclusions. 
Lefébure (1800), having finally accepted the conclusions of Séné- 
bier and Ingenhousz relative to the injurious influence of light on 
germination, repeated the experiments, but also observed the tem- 
peratures more carefully, and in addition sought to determine the 
effect of light that had passed through plates of white, green, black, 
red, and blue glass; but he added little to our knowledge, although 
he himself concluded that the seeds under white glass were retarded. 
Th. de Saussure (1804) endeavored to ascertain whether the influ- 
ence observed by others was due to light or heat, and he concluded 
that nothing demonstrates that light has an injurious influence inde- 
pendent of the heat that accompanies it. 
Keith (1816) made no observations himself, but controverted the 
conclusions of De Saussure. 
Boitard (1829) sowed the auricula seeds in three flower pots, but 
the conditions as to temperature and moisture are not sufficiently 
known to justify us in drawing any conclusion. 
A. P. de Candolle (1832) says: 
I do not deny that darkness may be useful in germination, but I do 
deny that it is necessary to think that light has no action on germina- 
tion. Analogy indicates this, theory confirms it, and experience dem- 
onstrates it. 
According to De Candolle, light favors the decomposition of car- 
honic acid, but germination demands the formation of carbonic 
acid; therefore darkness will favor germination. This theory 
thus enunciated by De Candolle has been accepted by many authors 
without proper experimental basis. 
Ch. Morren (1832) experimented upon water cresses grown under 
different colored glasses. He concluded that as darkness favored ger- 
mination, so the individual colors of the spectrum, acting each by itself, 
have a special influence that favors germination in such a way that 
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