96 Mr. Burnett on the Development 



though supplied with carbonic acid, provided the oxygen formed 

 by them during the day be constantly withdrawn at the approach 

 of night ;' and so on. Thus he treats of both changes as if the 

 effects of the same function, although it is not clear whether 

 that function is considered by him respiration or digestion, as 

 the term absorption is used in one place, and inspiration in 

 another. This statement is certainly much less perspicuous 

 than that of Ellis, but who nevertheless seems to have erred in 

 the doctrine he insisted on, viz., ' that this operation of affording 

 oxygen is not properly a vegetative function, but only a sub- 

 ordinate office ; for experiments have led me to conclude that 

 it is more essentially a vegetative function as depending on the 

 assimilation of the food, than even the respiration itself. 



Such being the state of the inquiry, several problems appear 

 to demand solution, and these we will shortly discuss in order. 

 1st, What are the changes produced by plants on atmospheric 

 air ? 2dly, Are these changes the effects of, and necessary to, 

 healthy vegetation ; or are they merely accidental to the vege- 

 table structure ? 3dly, Are these changes the varied results 

 of the same, or the unvarying results of different functions ? 



1st. What are the effects produced by, plants on ordinary 

 atmospheric air ? 



Experiments : Into 'several large wide mouthed stoppered 

 bottles, (the stoppers during all these experiments being fur- 

 ther secured by cerate, and in most instances inverted and the 

 necks placed under water,) leaves of sunflower, nasturtium 

 and other plants were severally introduced, and some put in 

 the sunshine, some in diffuse light, some in the shade, and 

 some enveloped in opaque coverings and kept wholly in the 

 dark. These bottles all contained, besides the leaves, ordinary 

 atmospheric air and a little water. At the end of six hours 

 they were tested with lighted tapers and with lime water. 

 The tapers were instantly extinguished when introduced into 

 those which had been kept in the dark ; in those bottles which 

 were standing in the shade, they burned but feebly ; while in 

 the two others they burned brightly, especially in those which 

 were exposed to the direct rays of the sun. Yet when the 

 untouched duplicates of these, were tested by means of lime 

 water, all of them without exception formed precipitates, 



