INTRODUCTION. 
XXV 
— he should have analyzed facts rather than assumed them. 
The small inquiring class, finding that this important link 
in the chain of argument is deficient, will be apt to think 
that the lapse of that single link sets adrift the entire cargo 
of conclusions. 
Having dismissed the gases with the alternative, that 
either they do not exist in any undue proportion in Mr. 
Ward’s fernery and its neighbourhood, or that they do 
exist, and are not injurious to vegetation ; having seen 
also that fuliginous matter does exist in the atmosphere to 
a great extent, that it is highly injurious to the growth of 
vegetables, and that it is excluded by Mr. Ward’s plan, we 
shall perhaps he expected, without further inquiry, to con- 
clude that in the exclusion of fuliginous matter rests the 
whole secret of its effect. To this I must demur, or the 
use of these closed cases would he confined to London and 
similar smoky atmospheres ; whereas it is well known the 
sphere of their utility is universal. Every cultivator in 
the country could adduce his proofs of this. I will cite 
one only. 
On a hot day in the summer of 1837, I brought home in 
a tin box about a dozen seedlings of Lastrcea multijlora, 
which I had picked out of moss ; each had a single frond 
of very small size, and extremely minute, white, and deli- 
cate roots. Having a wide -mouthed phial at hand, I put 
in it a small quantity of very wet earth ; and then passing 
a pin through the single frond of one of the seedlings, 
and pinning it to a cork previously covered with wet wash- 
leather, I fixed the cork firmly in the phial, and left the 
