GIuASS STRUCTURES. 



79 



against frost and far iDetter than stiuiters alone. The advantage 

 of having shutters in addition to the mats is that they keep the 

 mats from getting wet, which makes them so heavy that they 

 break easily in handling or they freeze solid and do not lie close 

 or are clumsy to handle. Rye straw is best for mats and it 

 is most tough and durable when cut partially green. It is often 

 threshed by hand so that the straw can be kept straight, but it 

 may be cleaned by a threshing machine by holding the bundle 

 and only putting the heads into the machine. 



Ventilation and Temperature are subjects of greatest impor- 

 tance 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 degrees in 

 the day and 40 to 50 degrees at night, and may even be frozen 

 without serious injury, while tomatoes, egg plants, cucumbers 

 and melons grow best at the higher temperature of 85 to 90 de- 

 grees in the day and 60 degrees 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, al- 

 though tomato plants will grow in quite cool temperature. In ad- 

 mitting air to glass structures care should be taken that the 

 wind does not blow in on the plants. This is generally best ac- 

 complished 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 ther- 

 mometer 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 makes 

 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 quite early in the 



