22 A MANUAL OF 



before they see daylight, and then the seller of 

 the seeds is lucky if he does not have to shoul- 

 der the blame and receive the charge of sell- 

 ing stale seeds. 



TEMPERATURE. Every hot-bed should have 

 one or more thermometers for showing at all 

 times the temperature of the bed, for it is ne- 

 cessary to the health of the plants that it does 

 not vary too much. Considerable variation is 

 allowable. The mercury may run from time 

 to time from 50 to 80 as extremes, though 

 the mean, which is 65, should be as closely 

 kept as possible. 



AIR AND LIGHT. The influence of light 

 and air is fully as necessary to healthy plant- 

 growth as it is to animals. If kept from 

 the light and air, a plant grows pale and spin- 

 dling ; still it is at all times necessary to guard 

 against too sudden an admission of air of a 

 different temperature from that within, as such 

 a change, or perhaps a continuance of a very 

 warm and wet atmosphere, with an occasional 

 admission of cold air, tends to produce what 

 is known as 



" DAMPING OFF" of the plants. This is a 

 shrivelling or wasting away of the body of the 

 plant just above the surface of the ground un- 



