42 VEGETATION. 



ent aspects of plants exposed to a free circulation of 

 air, and plants deprived of it ; the former are vigorous 

 and luxuriant ; the latter weak and stunted. It may 

 be seen also, by means of experiment, even upon a 

 small scale. If a plant is placed under a glass, to which 

 no new supply of air has access, it soon begins to lan- 

 guish, and at length withers and dies ; but particularly, 

 if it is placed under the exhausted receiver of an air 

 pump, as might be expected from the failure of the 

 germination of the seed, in similar circumstances. — 

 According to the experiments of Saussure, plants of 

 peas, though completely developed and furnished with 

 their leaves, died in the space of three days, when put 

 into the exhausted receiver of an air pu.mp, whether 

 in the shade or the sun. But even in this situation, 

 plants with thick and succulent leaves, seem capable of 

 supporting vegetation, at least if exposed to the sun. 

 A plant of the Prickly Pear, Cactus opuntia lived more 

 than a month in this state, without showing any symp- 

 toms of decay, except that the epidermis seemed dry, 

 which again recovered its freshness, however, in the 

 atmospheric air. 



But although we admit the great utility of atmospher- 

 ic air, and even its absolute necessity to the support of 

 vegetable life, we must not attribute to it more than is 

 due, and conclude without proof, that air, together with 

 water, forms the whole of the vegetable aliment And 

 yet in support of this doctrine, it has been said, that 

 many plants do evidently effect the developement of 

 their parts, without the' aid of any other nourishment 

 beyond that of air, rains, and dews ; and the Mosses 

 and Lichens, and some other tribes of plants, have been 

 quoted as affording examples. 



It must be admitted no doubt, that plants of slow 



