CARE OF PLANTS UNDER GLASS 67 



cover, two widths of heavy unbleached musHn are sewed together. 

 One edge of the cover is nailed to the top of the plank forming the 

 upper side of the frame, while the other edge is fastened to a roller 

 made by nailing together two 1' x 2' strips of wood in such a 

 way that the strips break joints and form a continuous roller as 

 long as the frame, except in the case of frames over sixty feet long 

 (Fig. 38), when the cover may be made in sections for convenience 

 in handling. The cover must be of such a width that when put 

 over the frame the cloth will come a little beyond the top of the 

 front plank. The weight of the roller will then hold the cover in 

 place. 



CARE OF PLANTS UNDER GLASS 



The first essential in the care of hotbeds, coldframes and green- 

 houses is the maintenance of the proper temperature for the wel- 

 fare of the plants. In the greenhouse the temperature is controlled 

 mainly by turning on or cutting off heating pipes, though venti- 

 lation is also used as a means of controlling the temperature, 

 especially late in the spring. Shading of the glass may also be 

 resorted to w^hen the weather becomes warm. In a fire hotbed, 

 the temperature is regulated by the extent of firing and also by 

 ventilation. In manure hotbeds and in coldframes the supply 

 of heat cannot be changed at the will of the operator. However, 

 the heat can be conserved or dissipated according to the needs of 

 the plants and the condition of the weather. On cold nights heat is 

 conserved by covering the sash with mats, shutters, straw or ma- 

 nure. During the day the sash may be raised to let out surplus heat. 



The object of ventilation, by opening the ventilators of green- 

 houses or raising the sash of hotbeds and coldframes, is not merely 

 to assist in the control of the temperature. It is even more im- 

 portant for changing the air in the house or bed. Fresh air should 

 be admitted every day. If the weather will permit, the sash or 

 ventilators should be left slightly open for several hours in the 

 middle of the day. Hotbeds require even more attention to venti- 

 lation than greenhouses, because the volume of air is so much 

 smaller. When the weather is so cold and windy that the hotbed 

 cannot be left open for any great length of time, it may be opened 

 slightly for a few minutes two or three times during the day, and 

 thus a change of air secured. This assists in drying out the bed 

 and preventing the damping-off of seedlings. Plants gro^vn with- 

 out sufficient ventilation are likely to be weak, spindling and sappy. 



