250 PRINCIPLES OF VENTILATION. 



accuracy of our assertion, for we find that all the highly devel- 

 oped organisms, such as we cultivate in our hot-houses, are only 

 adapted to exist where they can be daily invigorated by the 

 sun's rays. This fact is very strikingly illustrated in the effect 

 produced on tropical plants growing in hot-houses in the north- 

 ern latitudes, where, deprived of the intensity of the sun's rays, 

 under which they naturally luxuriate, they seem completely 

 changed by the long absence of the luminary on whose cheering 

 influence they depend. In such cases, no quantity or quality 

 of air will compensate for the loss of the sun's vivifying beams. 

 In the management of hot-house plants, the attentive ob- 

 server cannot fail to perceive the remarkable effects produced 

 upon certain kinds of plants by the circumstances in which they 

 are placed, as to heat, light, and air ; and hence the propriety of 

 arranging plants in hot-houses, not merely according to their 

 heights and colors, but also according to their habits and 

 requirements in relation to these elements.=^ Some plants will 

 endure an intensity of solar light, without injury, which would 

 utterly paralyze and suspend the functions of others; some will 

 luxuriate in an arid temperature, in which others would be 

 destroyed, and some require daily supplies of fresh air, while 

 others will exist even in a healthy state for years where the 

 atmospheric air is, one would think, almost excluded. Even 

 in nature there are many striking exemplifications of these 

 facts. A hot spring in Manilla islands, which raises the ther- 

 mometer to 187°, has plants flourishing in it and on its bor- 

 ders. In hot springs near a river of Louisiana, the tempera- 

 ture of which is from 122° to 146°, have been seen growing, not 

 merely the lower and simpler plants, but shrubs and trees. In 

 one of the Geysers of Iceland, which was hot enough to boil an 



* For example, the common weeds, called chickweed, groundsel and 

 Pea annua., evidently grow at a temperature very near that of 32^^, 

 while the nettles, and mallows, and other weeds around them, remain 

 torpid. In like manner, while our native trees are suited to bear the 

 low temperature of an English summer, and, in most cases, sutler 

 if removed into a warmer country, such plants as the mango and coffee- 

 tree, etc., inhabitants of tropical countries, soon perish, even in our 

 warmest weather, if exposed to the open air. — [Lind. The. of Hort.] 



