ADMrSSiaN OF AIR AND* LIGHT. 66b 



The quttntity of air to be admitted from time to time 

 must vary with tile seagon, the temperature required to 

 be kept up, and the kinds of plants cultivated. It should 

 be given and withdrawn by degrees, particularly in the 

 colder portions of the year. ' The sashes or ventilators, 

 for instance, may be partially open by eight A. M., top 

 air being given before front air ; full air may be em- 

 ployed about ten : a reduction should take place before 

 three P. M., and the whole should be closed betw<ien four 

 and five in the afternoon. In summer less caution is 

 necessary, as in many cases th« external air differs little 

 in temperature from that within the house. Most com- 

 monly air Is given only .during the day, arid is excluded 

 at night, with perhaps an increase of fire-heat. Judi- 

 cious horticulturists will sometimes reverse this process. 

 Knowing, for example, that in the West Indies chilly 

 and cold nights usually succeed the hottest days, they 

 will imitate, riature, by shutting up the house by day, 

 and throwing it open at night. This practice, however, 

 supported as it is by analogy, is subject to many limit- 

 ations, and can only be followed in our climate during 

 the summer and autumn inonths. It is useful, not- 

 withstanding, to remember the principle, though it ad- 

 mits only of partial application. ; 



The admission of Light. — In addition to the heat 

 with which natural light is always accompanied, there 

 seems to be another property necessary to vegetation, 

 which, from some cause hitherto unexplained, is partly 

 deranged by its transmission through glass. The fact, 

 however," is evident, from the circumstance that plants 

 thrive better near glass than at a distance from it, 

 though the intensity of light is apparently undiminish- 

 ed. Hence practical gardeners are anxious to distribute 



