A HISTORY OF SCIENCE 



the problem of respiration had been solved in its essen- 

 tials. Moreover, the vastly important fact had been 

 established that a process essentially identical with 

 respiration is- necessary to the existence not only of all 

 creatures supplied with lungs, but to fishes, insects, and 

 even vegetables in short, to every kind of living or- 

 ganism. 



ERASMUS DARWIN AND VEGETABLE PHYSIOLOGY 



Some interesting experiments regarding vegetable 

 respiration were made just at the close of the century 

 by Erasmus Darwin, and recorded in his Botanic Gar- 

 den as a foot-note to the verse: 



"While spread in air the leaves respiring play." 



These notes are worth quoting at some length, as 

 they give a clear idea of the physiological doctrines of 

 the time (1799), while taking advance ground as to the 

 specific matter in question: 



"There have been various opinions,*' Darwin says, 

 " concerning the use of the leaves of plants in the vege- 

 table economy. Some have contended that they are per- 

 spiratory organs. This does not seem probable from an 

 experiment of Dr. Hales, Vegetable Statics, p. 30. He 

 found, by cutting off branches of trees with apples on 

 them and taking off the leaves, that an apple exhaled 

 about as much as two leaves the surfaces of which 

 were nearly equal to the apple ; whence it would appear 

 that apples have as good a claim to be termed per- 

 spiratory organs as leaves. Others have believed 

 them excretory organs of excrementitious juices, but 



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