the seeds in the shade to germinate soo'ner than those 

 in the light *. The more equable warmth which 

 seeds preserve, when excluded from the direct con- 

 tact of light, may be a principal reason why they 

 grow best in the dark ; and the evaporation which 

 takes place on exposure, to which the Abbe al- 

 ludes, would not only deprive the seed of the wa- 

 ter essential to its growth, but be at the same time 

 a considerable source of cold. In many trials we 

 found, that steeped seeds, when exposed in the open 

 air, rapidly lost their moisture, and made no effort 

 to germinate ; but the same seeds, when confined in 

 a glass-vessel, so as to check the progress of evapora- 

 tion, germinated freely, though exposed to the same 

 temperature, and the same degree of light. Hence 

 we infer, that light, simply, has little influence either 

 in promoting or retarding the germination of seeds. 



4. But although water and heat appear to be the 

 only agents essential to the beginning of germina- 

 tion, yet after a certain period air becomes equally 

 necessary. Mr Boyle, Ray, and many other philo- 

 sophers, ascertained that seeds would not grow in 

 the vacuum of an air-pump.. Some lettuce-seeds 

 were sown upon earth in the open air, and some of 

 the same seeds, at the same time, on another portion 

 of earth placed in a glass-receiver, which was after- 

 wards exhausted of air. The seeds exposed to the 

 air grew nearly an inch and a half high in eight 

 days ; but those in the exhausted receiver not at all. 

 Air, however, being now admitted into the receiver, 



* Thomson's System of Chemistry, vol. iv. p. 236. 1st Edit. 



