GLASS STRUCTURES 111 



holding the bundles and putting the heads only into the 

 machine. 



Ventilation and temperature are subjects of greatest 

 importance in growing plants under glass. The various 

 classes of plants require different degrees of heat to reach 

 their best development. For instance, lettuce, radish, 

 cress, and similar plants grow best at a low temperature, 

 say about 75 F. in the day and 40 to 50 at night, and 

 may even be frozen without serious injury; while tomatoes, 

 eggplants, cucumbers, and melons grow best at the higher 

 temperature of 85 to 90 in the day and 60 at night. If 

 the former plants are kept at a higher temperature than 

 that given they are liable to become diseased and infested 

 with insects. This is especially true of lettuce. On the 

 other hand, if the high-temperature plants are kept much 

 cooler they become sickly and weak, although tomato plants 

 will grow in quite cool temperature. In admitting air to 

 glass structures care should be taken that the wind does 

 not blow in on the plants. This is generally best accom- 

 plished in hotbeds and frames by blocking up the sash at 

 the ends or sides with notched pieces of wood. 



The temperature of any place, unless otherwise specified, 

 is the temperature there of a thermometer in the shade. A 

 thermometer with the full sunlight shining on it will record 

 about fifteen degrees higher than in the shade, which is a 

 point always to be borne in mind in ventilating. 



In the weather of early spring when the sun is getting 

 high, the middle of the days will be very warm and the 

 nights still quite cool and frosty. It is then that a beginner 

 often mal es the mistake of leaving the sashes of his hotbeds 

 open late in the afternoon, and the beds cool off more than is 

 desirable. At this season of the year but little ventilation 

 is necessary, and frames and greenhouses should be shut up 



