18 BRITISH FERNS. 
the uniformity and excess of atmospheric humidity ; 
in the absence of extremes of heat and cold; and, 
if these extremes must occur, in the gradual transi- 
tion from one to the other; and finally, in that 
perfect stillness of the atmosphere which is to be 
found only in caves, fissures of rocks, wells, and a 
few similar situations. 
Now it has long been known that a covering of 
glass is the best artificial substitute for Nature’s 
care: from time immemorial the gardener has been 
aware of this, and has most cleverly availed him- 
self of the knowledge; the hothouse, the green- 
house, the conservatory, the pinery, the melon-pit, 
the cucumber-frame, the Propagating-glass, nay, the 
very hand-glass that we see so abundantly in our 
market-gardens, are so many unquestionable wit- 
nesses to the early use of glass for this very pur- 
pose; in fact, there is reason to believe the use of 
the hand-glass is almost coeval with the invention 
of glass itself, ‘To Mr. Ward we are indebted for 
bringing the hand-glass into our halls and our 
drawing-rooms, for placing it on the window-sills of — 
our chambers, and for making yast improvements in . 
