226 
CULTURAL CHEMISTRY. 
moistened with rain-water, and in it he planted a willow, which then weighed 
2 1 kilogrammes (the kilogramme is equal to 2.205 pounds avoirdupois). During 
five years the earth was carefully watered with rain or pure water (?). In order to 
prevent the access of any other mould, as dust or otherwise, the surface was covered 
with a flat metal plate, pierced with a great number of small holes, so as to permit 
nothing to pass but the atmospheric air only. At the end of the five years the tree 
was taken up, and its weight ascertained to be about 85 kilogrammes, amounting to 
some decimal parts above 187 avoirdupois pounds! The earth redried in an oven 
and weighed, was found to have lost 60 grammes only, or something under 930 
grains. Thus,” it is observed, “nearly 80 kilogrammes of woody fibres of bark and 
of roots were found to have been produced ! In giving this recent experiment, 
which we borrow from an English journal, and which had already been performed 
more than two centuries before by Van Helmont, one of the great chemists of the 
day, we recall to recollection that within a few years past our own learned chemists, 
and the German Liebig, have published many others of a similar character, 
and which, to say the least of them, are equally interesting.” (See “ Illustration,” 
Sept. 30.) 
There is much plausibility in the inference at which modern theory arrives ; we 
go farther, and admit that experiments so arranged tend very forcibly to confer 
weight on the hypothesis that plants do, in fact, absorb gaseous carbonic acid, which 
exists in the air. Still, however, it must not be overlooked that rain-water contains 
that gas, as well as a trace of ammonia, and some pure carbon, as is evidenced by 
the stain which rain-drops leave upon glass. Moreover, air is not excluded ; it passed 
through the perforations of the metallic covering, and air abounds with gaseous 
admixtures. Hence, every application of water would convey nutritive solutions to 
the soil. But it is not our object to impugn the doctrine of absorption in toto. 
Leaves have vascular pores, and some possess them on both surfaces — the microscope 
assures us of the fact — and skilful dissection has demonstrated their connexion with 
the internal tissues. The air, we perceive, abounds with gases independent of its two 
chief constituents, and immense volumes of aqueous vapour, carbonic acid, ammo- 
niacal and hydrocarbonous gases, are daily and hourly poured into its volume from 
the surface of the earth ; therefore we would incline to the belief that plants may 
attract such aerial matters as are congenial to their organisation, thus purifying the 
air by the removal of deleterious vapours. But belief is not assurance, and when 
we perceive that philosophers adopt a mode and apparatus of experiment at variance 
with the natural functions, we must hesitate still more. 
If, however, we are not sure that leaves inhale, we are perfectly certain that they 
transpire, by their under surfaces at the least, if not by both. On this function (of 
which every observant gardener possesses positive evidence) Mr. Johnston offers the 
following pertinent remark in his Lecture : — 
“ From the pores of the leaves, odoriferous and other vapours, as well as liquids 
exude. Need I remind you of the odour of a turnip-field when the bulbs have 
