66 THE IMITATION, IN CLOSED CASES, OF 
close method of growing plants consist mainly 
in the power we possess of freeing or sifting 
the air from extraneous matters, of imita- 
ting the natural condition of all plants, as far 
as the climate we are living in will enable us 
to do, and of maintaining this condition for 
indefinite periods, free from disturbing causes. 
The plants are, of course, preserved from excess 
or deficiency of moisture, and owing to the 
perfectly quiet condition of the atmosphere 
with which they are surrounded, are able, like 
man, to bear extremes of temperature with im- 
punity, which under ordinary exposure would 
destroy them. The experiments of Sir C. Blag- 
den, 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 undis- 
turbed, and thus acting as a protecting shield. In 
like manner the Trichomanes lived for three years 
in a window with a southern aspect, exposed 
continually to a heat, which, without the pro- 
tection afforded by the glass, would have de- 
stroyed it in a single day. "With respect to cold, 
the concurrent testimony of all arctic voyagers 
proves, that no inconvenience is felt, provided 
the air be perfectly still, even if the thermometer 
