214 Remarks on Objections to Experiments on Vegetation. 
the experiments relative to the effects of vegetation, &c. on at- 
mospherical air, communicated to your Magazine of July; but 
also to those of Mr. Ellis, which he says ‘¢ are as liable to objec- 
tions as any other.” - 
He disapproves of the “ mercurial effluvia,” without proving 
that such existed in the experiment, at least so as to retard the 
functions of the plant, for there was but about two or three inches 
surface of mercury exposed to the air of the plant (but as [ be- 
lieve Mr. Ellis did not use mercury in his experiments, he is not 
liable to this objection). To the “ confined instead of a free 
atmosphere” he also objects; and then concludes by stating, that 
he holds unchanged ‘ the opinion he has long maintained as to 
the direct experiments of Drs. Priestley and Ingenhousz, since 
corroborated, namely, that the quantity of carbonic acid evolved 
by plants will bear but a pitz?ful proportion to the floods of oxy- 
gen poured out upon the atmosphere by the exercise of the ve- 
getable function.” 
Now, I would ask the objector what were the direct experi- 
ments of Drs. Ingenhousz and Priestley, and by whom and how’ 
since confirmed, which have so confirmed or established him in. his 
opinion?» Was it the experiment of Dr. Ingenhousz, as related 
at page 14 of his work? where he says: “ they (the detached 
leaves) are to be put in a very transparent glass vessel, or jar, 
filled with fresh pump water, (which seems best adapted to pro- 
mote this operation of the leaves, or at least not to obstruct it,) 
which being inverted in a tub full of the same water are to be 
exposed to the sunshine: thus the leaves continuing to live, 
continue also to perform the office they performed out of the 
water.” 
Is this experiment of the unnatural situation of detache leaves 
less objectionable than the one in which an entire plant, or spring 
while attached to its parent, is placed in atmospherical air? Should 
Mr. Murray think so, I shall still, whenever J wish to ascer- 
tain the effects of a plant (not an aquatic one) on the atmosphere, 
always place it in atmospherical air, and not in water; and shall 
always prefer using an entire plant, or that part of one attached 
to its parent, rather than de/ached leaves. 
As for the “ floods of oxygen’’ which he says are ‘* poured out. 
upon the atmosphere by vegetation, being so superior to the 
pitiful quantity of carbonic acid; this remains to be proved; for 
I do not recollect one experiment cither of Drs. Ingenhousz, 
Priestley or others, which is adequate to it, And although he 
is such a strenuous advocate of Dr. Priestley, he must. acknow- 
ledge that the Doctor’s experiments frequently proved the con- 
trary; for at p. 336 of his third volume, the Doctor states “¢ that 
the air in which a willow plant was growing, continued to de. 
crease 
