PART III. VENTILATION. 



SECTION I. 



PRINCIPLES OF VENTILATION. 



1. The ventilation of hot-houses, either in summer or win- 

 ter, constitutes an important, if not the most important, item of 

 their general management, as it bears more directly upon the 

 condition of the external and the internal atmosphere. It re- 

 quires, therefore, the strictest attention of the gardener at all 

 seasons of the year. For, important as other things connected 

 with exotic horticulture may be, — light, for instance, — it is, 

 nevertheless, more under the gardener's control, and more sub- 

 ject to his will. He places his plants within a transparent 

 medium, which is, in its general surface, impermeable to the 

 atmospheric air; and he forms for them an artificial atmos- 

 phere, which is invigorating, or the reverse, according to his 

 knowledge of the laws that regulate the atmosphere, or the 

 general principles of aerometry. Notwithstanding the many 

 discoveries that have been made regarding the properties of air, 

 I have been unable to find any work bringing these discoveries 

 to bear upon the airing of hot-houses. It is true this must be 

 accomplished by the " practical " man, and the sooner we begin 

 to think about it the better. Every horticulturalist, no matter 

 what his department in the vineyard may be, soon discovers the 

 necessity of maintaining a continual warfare with its different 

 conditions of purity and impurity, its aridity, and its moisture. 

 We have, indeed, various theories propounded by physiologists, 

 regarding the power of plants to withstand these vicissitudes, 

 some of which have their general principles as yet enveloped in 

 a mist of shadowy vagueness. 



Many remarkable facts, however, might be mentioned relative 



