109 
Ventilation must, ofcourse, be provided in some way, whether 
the drill cover be glazed or opaque. Indeed, in the latter case 
it would be advisable to cause a portion of the roof, nearest the 
apex, to open from one end of the drill cover to the other, longi- 
tudinally. By this arrangement, light would be uniformly ad- 
mitted, as well as air, when mild weather occurred. The roof 
may, in that case, be composed of two feather-edged boards, of 
about five or six inches each in width, the upper over-lapping 
the lower one; the upper having a hinge at each end, and, of 
course, opening perpendicularly to the apex. The two venti- 
lating lids in giving air would thus meet above the apex, and 
might be secured by a hook and staple. This would indeed be 
perhaps the most economical mode that could be devised, and 
we do think that every small garden in the country should pos- 
sess at least half a dozen. As an adjunct to the little green- 
house too, they would at certain seasons be invaluable. Half- 
hardy plants might, with facility, be wintered in them, merely 
by having them well established in store pots, and by keeping 
them dry ; the addition of a mat, or some coarse litter, would 
thus carry the inmates through the hardest frosts. They would 
be well adapted for a small mushroom bed also; and, in this 
case, it would be very easy to apply a warm dung lining on 
each side, when the weather was severe. Many other things 
belonging to the greenhouse will readily suggest themselves ; 
even when the Vines commence their growth, when extra 
warmth becomes essential, and when so many good plants are 
thereby sure to become ‘drawn,’ a considerable amount of 
stock might be thinned out and placed beneath the drill covers, 
thus affording more room for good specimens, as well as for 
manual operations in the greenhouse. 
With regard to the glazed drill covers, we need scarcely urge 
their general superiority, at least during the growing season, for 
it must be always understood that the amount of light must, in 
nearly all cases, bear a strict relation to the rapidity of growth. 
When such relations are disturbed, or the light intercepted from 
an active vegetation, what is technically termed ‘ draw ing ’ takes 
place. This is, we conceive, familiar to every one ; a potato 
left in a comparatively dark cellar, late in spring, will afford a 
pretty good illustration of this. Although there are cases, 
especially in the wintering of plants, when the opaque drill cover 
295. ACCTARIUM. 
