90 BIOLOGY OF PLANTS. 



diminishes ; hence, plants which grow on high mountains, 

 receive less of the support above mentioned. It may be due 

 to this circumstance, that plants w\\\\ fleshy leaves flourish best 

 in such regions. 



2. The atmosphere not only furnishes food and support to 

 vegetables, but it is the medium of communicating nourish- 

 ment, and for the action of other agents. It is by the agen- 

 cy of the atmosphere that water is borne up from the ocean, 

 and distributed to every part of the land, in the form of rain 

 and dew, — that carbonic acid, ammonia, odoriferous and sa- 

 line particles are conveyed to the organs of plants. Its per- 

 fect elasticity, yielding to the slightest pressure, and its con- 

 stant motion, give to plants their proper exercise, without the 

 slightest injury. It is the medium for the agency of light, 

 heat and electrical changes, which are intimately connected 

 with the vital functions of plants. Bearing, as it does, the 

 clouds on its bosom, it furnishes an opportunity for some of 

 the most sublime and beautiful phenomena of the natural 

 world. 



The influence of the moisture of the atmosphere will be 

 considered in the next section. 



Such are the elements of our atmosphere, and their import- 

 ant influence upon the vegetable kingdom. Its constitution 

 and properties render it beautifully and wisely fitted for its 

 indispensible agency. The manner in which its elements are 

 combined, exhibits, in a striking light, the wisdom and be- 

 nevolence of the Creator. The oxygen, nitrogen, and other 

 gaseous bodies, of which the atmosphere is composed, seem 

 not to be governed, as they are in other combinations, strict- 

 ly by the laws of chemical affinity, or of mechanical mixture. 

 Its constitution appears to be an exception to general laws, 

 for the special benefit of the animal and vegetable kingdoms. 

 Its elements obey nearly the laws of combination, which they 

 observe when they combine in other proportions ; and yet, 

 they are so loosely united to each other, that each seems to 



