4-40 hifluence of Climate on Vegetatioit. 



flowers perish ; dry fruits appear ; and, presently, nothing 

 remains to view except plants with either hard and dry, or 

 extremely succulent leaves, to enable them to absorb moisture 

 from the atmosphere, and to impede too rapid an evaporation 

 during the dry months. 



In Mexico, the climate is generally temperate ; but the 

 mountainous parts differ very considerably from the plains. 

 Bagdad is subject to variations of intense heat and cold, and 

 occasionally to heavy rains. 



In the polar regions, where there is perpetual light during 

 six months of the year, and darkness during the remainder, 

 the plants are weak and stunted. They grow slowly ; and 

 trees, large in other countries, dwindle down to the size of 

 shrubs. 



Besides the differences of climate already enumerated, there 

 are other circumstances which require the attention of the 

 gardener. One is the effect produced by the pressure of the 

 atmosphere. Mountain plants will not thrive well in plains ; 

 and will die there, though enjoying exactly the same heat as 

 in their native countries. Light, it has been already shown, 

 has a very material influence on vegetation. When exposed 

 to it, plants give out their oxygen, and evaporation proceeds 

 rapidly. Mountain plants are generally covered with snow 

 during winter; and thus enjoy a season of complete repose, 

 and equal temperature, in darkness. When plants thus ha- 

 bituated are long exposed to the light, they are too much 

 excited, and become so feeble as to be unable to resist the 

 cold. Experiments have been tried for keeping alpine plants 

 in darkness during winter, which have proved successful. 



Almost all plants require alternate seasons of repose and 

 growth ; and many, if forced too much, and kept continually 

 growing, will die. As an instance of the power of rest: from 

 accidental circumstances, a plant, generally difficult to flower, 

 was found to grow 7 ft. high in one season, and was covered 

 with thousands of blossoms. The plant had been forced very 

 rapidly; and afterwards, in order to make room for others 

 coming into flower, put away in a dark place, and completely 

 neglected for several months. It had thus a complete period 

 of rest; and, when again forced, it blossomed profusely, as 

 before stated, and was never seen finer in China. Nothing 

 can be more at variance with the ordinary practice of gar- 

 deners than this treatment: it is, indeed, impossible, where 

 plants from different countries, and, of course, habituated to 

 different climates, are all mixed together in one house. Plants, 

 when in a state of repose, have also an untidy and desolate 

 appearance ; very annoying to gardeners, who pique them- 

 selves on their plants always looking well. 



