DIFFERENT FORCING HOUSES. 249 



would recommend fresh air to be admitted into 

 the house every day, unless the frost is in- 

 tensely severe, or the air so saturated with fog, 

 or otherwise filled with humidity, that it is 

 really dangerous ; otherwise, if it is but five 

 minutes in the day, with merely a crack here 

 and there at the top, to let out a little of the 

 confined air, it will be of service to the plants ; 

 and during the early part of the forcing, from 

 half an hour to an hour, or from that to two, in 

 the middle of the day, being guided by the 

 warmth of the external atmosphere, and em- 

 bracing as much as possible the opportunity 

 when the sun shines ; but still, at the early part 

 of the forcing, the air should be admitted spar- 

 ingly, by sliding open some of the glasses only ; 

 but, as the season advances, and the sun has 

 proportionate influence, so should the admis- 

 sion of air increase from eleven till two or three ; 

 and in very warm weather, and the power of 

 the sun is great, the house may be opened 

 earlier in the morning, and shut later in the 

 afternoon, and so be guided according to the 



M5 



