“PHYSIOLOGY. geN9 
be called, of plants, was first discovered by Bonnet 
in the year 1754; after him more accurately observ- 
ed by Priestley in 1773, who was followed in 1779 by 
Ingenhouss, and soon by many other celebrated chy- 
- mists,’ of which we shali only mention Sennebier, 
Scheele, Achard, Sherer and Succow. No branch 
of the Physiology of plants has been examined with 
more numerous experiments. We shall not at 
present repeat all those, which confirm the pheno- 
menon of transpiration in vegetables, and which 
throw new light on the whole Physiology of the 
vegetable kingdom ; the various results will suffice, 
which are to be deduced from such minute and 
careful experiments. 
Plants in general, but particularly their leaves, 
emit oxygen gas, when exposed to the sunshine ; at 
night time, however, during darkness, they exhale 
carbonic acid gas. At sunshine the pine-tribe, the 
gramina, and many of the succulent plants, exhale a 
vast quantity of oxygen gas. The leaves of trees 
emit less of it than herbs. No oxygen gas what- 
ever, even when exposed to the sun, is exhaled by 
flex aquifolium ; Pranus laurocerasus ; Mimosa sen- 
sitiva, Acer foliis variegatis, the petala, ripe fruits, 
the bark of trees,.the footstalks or the fibres of 
leaves. The gas which is emitted during night is 
by far less in quantity, and not in all plants pure 
carbonic acid gas, but often mixed with azote and 
hydrogen. It is scarcely necessary to remark, that 
in the great number of plants the modifications of 
hese gases are various. 
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