Rev. P. Keith on the Conditions of Life. 129 



The same condition is necessary to the vegetating plant* 

 Grew having discovered, in a leaf that he was examining, a 

 number of little bags or bladders, filled as he thought with 

 air, drew the conclusion, and maintained the doctrine, that 

 leaves are the lungs of plants. M. Papin, with a view to as- 

 certain the point in question, introduced into the receiver of 

 un air-pump an entire plant, root, stem, and leaf: the con- 

 sequence was, that it very soon died. He then introduced a 

 plant by the root and stem only, with the leaves and branches 

 exposed to the influence of the atmosphere : still the plant 

 died after a while; but it lived much longer than in the former 

 case, and warranted him in concluding, as he thought, that leaves 

 are indeed the lungs of plants*. Whether this conclusion 

 was legitimately drawn from the premises, or noi, we will not 

 at present stop to inquire. Enough was done to show that 

 plants cannot continue to live without the access and contact 

 of atmospheric air. They will not even grow with vigour 

 unless they have an abundant supply; as he who has the ma- 

 nagement of a hot-house too often discovers to his cost. The 

 plant that grows where there is no free circulation of air springs 

 up slender and sickly. The plant that is exposed to the action 

 of the stormy blast springs up stout and robust. 



Of the truth of the same conclusion as applicable to animals, 

 it will scarcely be necessary to offer any formal proof. It comes 

 so completely home to every one's own experience, that he 

 must be a bold man who would deny it; yet if proof were 

 wanted, it would be found in the death of many a poor mouse 

 that has been placed in the receiver of an air-pump for the 

 purpose of experiment. 



There are, it is true, some apparent exceptions to the above 

 rule. It has been said of the Truffle, that it vegetates without 

 the access of air, because it vegetates wholly under ground. 

 But it is very well known that air penetrates the soil to a depth 

 beyond that at which the Truffle is found. It does not there- 

 fore vegetate without aiiration. For the same reason it has 

 been thought that the roots or bulbs of plants whose stem dies 

 down to the ground in the winter must needs vegetate without 

 air. Bui air is conveyed to them in the moisture of the soil ; 

 and of some of them it may be said that they hybernate rather 

 than vegetate in the winter : at any rate they are not deprived 

 of the access of air f . But it is in the animal kingdom that the 



excep- 



• Phyx. (lex Arb. liv. ii. chap. '■S. 



f [We may add, iti confirmation of this reasoning, that it has been ahovvn 

 by Mr. Bowman, (Trans, of Linn. Soc. vol. xvi. \yAVS, &c.) that the squa- 

 ma: of the subterranean stem of Luthram xrjnainaria are real leaves and 

 organs of ai ration. Hut the same botanist remarks, that Cuscnta, Listcra 

 N. 6". Vol. 1 0. No. 5G. Aw'. 1831. S A';'<'«» 



