326 GENERAL REMARKS ON THE MANAGEMENT 



is effectually intercepted, and the atmosphere preserved from 

 excessive moisture. 



The difficulty of keeping succulent plants in damp cellars, 

 during winter, is also owing to the same cause. Moisture, 

 without a sufficiency of light to enable plants to decompose it, 

 quickly destroys them. 



On the other hand, the difficulty of keeping up that necessary 

 degree of humidity in the atmosphere of a dwelling room, dur- 

 ing the summer months, is the cause of the unhealthiness of 

 plants kept in them ; and the fact of their position being gener- 

 ally in the window, where there is always a current of air from 

 without, during the day, contributes, in a great measure, to 

 exhaust the plants of their contained moisture, and then they 

 gradually decline. Could the atmosphere around them be kept 

 sufficiently moist, with plenty of light, there is no reason why 

 they should not thrive as well as in the green-house. 



We have already alluded to the injurious effects of maintain- 

 ing a high temperature in green-houses and conservatories dur- 

 ing winter. If we look over the different climates of the world, 

 we shall find, that in each there is a season of growth, and a 

 season in which vegetation is more or less suspended, and that 

 these periodically alternate with the same regularity as our 

 summer and winter. I do not know that in nature there is any 

 exception to this rule ; for even in the Tierra Templada of Mex- 

 ico, where, it is said, that, at the height of 4000 to 5000 feet, 

 there constantly reigns the genial climate of spring, which does 

 not vary more than 8 or 9 of temperature, intense heat and 

 excessive cold being alike unknown, the mean temperature 

 varying from 68 to 70; we cannot suppose that, even in 

 that favored region, a season of repose is wanting; for it is 

 difficult to conceive how plants can exist, any more than animals, 

 in a season of incessant excitement. Indeed, it is pretty evident 

 that these countries have periods when vegetation ceases, for 

 Xalapa belongs to the Tierra Templada, and we know that the 

 Ipomea purga, an inhabitant of its woods, dies down annually, 

 like our native Convolvuli. 



From what has already been said on this subject, it is evident 

 that the natural resting of plants from growth is a most impor- 



