43 



that up to that time it had not been proven whetlier the germination 

 of the seeds was att'ected by light or by humidity. His own experi- 

 ments convinced him that the hitter was more important. 



Senebier (1800) maile acUlitional experiments on peas and beans, 

 sowing tliem in sponges, which were kept equally moist, all inclosed 

 under 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, 

 Leclerc (1875) has shown that under the influence of mercurial 

 vapor, as it existed in Senel)ier's experiments, a large portion of seeds 

 are killed, so that with our present knowledge we can not accept 

 Senebier's conclusions. 



Lefebure (1800), having finally accepted the conclusions of Sene- 

 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 w^ere retarded. 



Th. de Saussure (180-1) 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 (18*29) 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 (188-2) says: " 



I do not deny that darkness may be useful in germination, but T do 

 deny that it is necessary to think that light has no action on germina- 

 ti(m. Analogy indicates this, theory confirms it. and experience dem- 

 onstrates it. 



According to De Candolle, 'light favors the decomposition of car- 

 l>onic 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 

 Avithout 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 hy itself, 

 have a special influence that favors germination in such a way that 



