APPENDIX A. 
409 
There are many other situations where these cases would he useful, as. on 
ship-board or in other places where there exists a necessity for economizing 
water, or in very cold countries, where it is equally necessary to make the best 
use of the little sun they possess and to protect the plants from cold winds. 
The cabbages of Iceland and Labrador would surely exceed their present size 
of about one or two inches in diameter if thus protected. 
To conclude with a few general observations. 
The advantages of this method of growing plants consist, first, in the power 
we possess of freeing or sifting the air from all extraneous matters ; — then of 
imitating the natural condition of all plants, as far as the climate we are living 
in will enable us so to do ; and of maintaining this condition free from those 
disturbing causes to which plants are oftentimes subjected from sudden varia- 
tions of weather. They are preserved of course from the excess or deficiency 
of moisture, and, owing to the perfectly quiet atmosphere with which they are 
surrounded, they are able, like man, to bear extremes of heat and cold with 
impunity, which in ordinary circumstances would destroy them. The experi- 
ments of Sir Charles Blagden and others, in heated ovens, are well known, and 
the performances of Chaubert are familiar to most of my readers. In these 
instances the immunity is owing to the aqueous exhalations from the surface of 
the body remaining undisturbed, and acting as a protecting shield. In like 
manner the Trichomanes lived for three years, in a window with a southern as- 
pect, exposed continually to a heat which, without the glass, would have 
destroyed it in a single day. With respect to cold, the concurrent testimony 
of all arctic voyagers proves that no inconvenience is felt, even at 70“ below 
zero, provided the air be perfectly still ; but, that if wind arose, although the 
thermometer generally rose rapidly with the wind, the cold then became insup- 
portable. We need not go to the Pole for illustrations of this fact. Every 
one has felt the difference between walking with his face or his back to one of 
our east winds in March, those winds which are often so destructive to vegeta- 
tion in the open air, but have not the slightest effect on enclosed plants. I 
need not say anything respecting the change of air, as, from the contents of the 
preceding chapter, it must be obvious that as soon as any gas is generated 
within the case different to the atmosphere without, diffusion immediately com- 
mences, and no mode of closing the cases which I have adopted can prevent 
this from taking place. 
As regards the cases in which these plants are grown, their shape or size may 
be adapted to the situations in which they are to be placed. The best cover for 
the smaller ones is, 1 think, the oiled silk of which bathing-caps are made, or 
in wild luxuriance, producing, notwithstanding they are so shaded, the most delicious fruit. And 
here, while the eyes are fed with the endless variety of flowers which deck these sylvan scenes, the 
ears are at the same time ravished with the melodious notes of numerous birds, which are attracted 
to these groves by the cool springs and the food which they there find.” — A'idd’s Bridgewater 
Treatise. 
