34 DREER’S VEGETABLES UNDER GLASS. 
of economy of time, is explained in the chapters on lettuce 
and cucumbers. 
A great help in the matter of changing the soil of these 
great houses is the small door on the north side of the house, 
as herewith shown. A line of these doors extends from end 
to end of the forcing house, being cut through the double 
wall of boards on the cold side of the building. The doors 
are, of course, permanently closed during the winter. 
GLASS DOORS OR VENTILATORS, NEAR GROUND, ON WARM SIDE OF 
BOSTON FORCING HOUSE. 
‘ 
On the southern side of the house, below the ‘‘square”’ 
or pitch of glass, a number of glass doors or ventilators are 
placed. ‘These doors or gldss windows swing outward, being 
hinged on their upper edges, and are used during any time 
of the year, whenever required by the temperature of the 
house. ‘These ventilators, in connection with others at the 
peak of the glass roof, aid in producing a perfect circulation 
of air above the plants growing inthe beds. The ventilating 
