56 SCHOOL AND HOME GARDENING 



heat for the hotbed: (1) The rotting manure in the hottom of 

 the bed causes a great deal ol' heat which warms the soil, plants, 

 and air of the bed. (2) The bright rays of the sunrihine 

 through the clear glass without warming the glass ; but these 

 bright rays striking the soil and plants inside the bed are 

 changed to " dark " or obscure rays ; these dark rays will not 

 again go through glass readily. Thus the rays of the sun enter 

 the bed, are trapped by being changed in character, and do 

 not readily escape. 



By these two methods of heating, a bed may become warmed 

 too much even on cool days. It is partly for this reason that 

 covers or shades are used and that ventilation is used. 



Coldframes and Hotbeds Compared. — Coldframes may 

 be of the same construction as hotbeds, with the exception of 

 the fresh manure. No heat from the bottom is used in a cold- 

 frame. The glass of the coldframe is kept covered in cold 

 weather with matting, carpeting or other material to keep out 

 the wind. Of course, with hotbeds, such protection is also 

 used on cold nights and cold, cloudy days, but the glass is 

 uncovered on bright days to admit the rays of the sun through 

 the glass. 



Operating a Hotbed. — There are a number of special 

 things to attend to while running a hotbed. 



The temperature must not become too hot nor too cold 

 at any time. Some variation in temperature between night 

 and day must be expected. A thermomeiter should be kept 

 in the hotbed so that the operator will not need to guess as 

 to the temperature. Some plants, as radish, lettuce, beets and 

 carrots, are best suited by cool conditions and others need to 

 have the soil and air warmer, as tomatoes, egg-plants and 

 peppers. So no rule can be established as to an e.xact tempera- 

 ture for all plants. Those plants which are mentioned a-s 

 being hardy enough to endure late spring frosts are the plants 

 which thrive better when the day heat in the bed does not 

 exceed G()° or 70° Fahr. The summer or " hot weather " plants 



