THE NATURAL CONDITIONS OF PLANTS. 45 
plants might'' be intermixed with the ferns, and 
would add greatly to the effect of the whole, 
taking especial care that each should have the 
amount of light and moisture which it obtains in 
its natural state. 
So much for British ferns and plants ; hut the 
time will most assuredly come when those citizens 
of London who now recreate and refresh their 
souls with such a house as is above described, will 
raise their desires to the possession of equally 
beautiful, hut much more noble and majestic 
forms : I mean, particularly, those of the Tree 
ferns. We are told by Humboldt, that between 
the Tropics, on the declivities of the Cordilleras, 
the proper zone of the Tree ferns is between 
3200 and 5330 feet above the level of the sea. In 
South America and the Mexican Highlands, they 
seldom descend lower than 1200 feet. The mean 
temperature of this happy zone is between 10'2 
and 64’6 Fahr. This region enters the lowest 
stratum of clouds, or that which floats next 
above the sea and the plains ; and hence, besides 
great equality of temperature, it enjoys, unin- 
terruptedly, a high degree of humidity. The 
conditions of mild temperature and an atmosphere 
nearly saturated with vapour, are fulfilled on the 
declivities of the mountains in the valleys of the 
Andes, and, above all, in the mild and humid 
