36 



observation he had made, of considerable interest and im- 

 portance, which be bebeved bad liitberto escaped the notice of 

 other enquirers. 



" A leaf of vabsneria was examined, the distal end of which 

 (that . .rtbest from the plant) appeared perfectly dead and brown. 

 In tins portion, circulation was going on vigorously, in every 

 cell, while in those parts wbose vitality was undoubted, and 

 where the colour was green, and the air passages filled with 

 gaseous matter, no circulation was to be seen. This observa- 

 tion he bad made repeatedly upon dying leaves, and had 

 always found motion in the dead, but none in the living parts. 

 In confirmation of this, he then exhibited portions of leaves, 

 that bad been cut off three weeks previously, some of which 

 had become perfectly brown and apparently dead. In these 

 parts the cells were much reduced in size, the globules had 

 lost their greenness, and were diminished in size and numbers 

 very considerably. The nucleus was, however, clear and 'of 

 the usual magnitude. It was a very remarkable fact, that the 

 prussic acid had the same effect upon these dead leaves as upon 

 the living ones. That is, the circulation was stopped by its 

 application, but renewed again after immersion in pure water." 



He then proceeded to enquire into the question — Whether 

 the circulation was produced by physical or by vital causes ? 



"The chief grounds on which a physical cause might be 

 presumed, were, that in the vabsneria, the motion did not 

 exist so extensively in the growing plant, as in parts cut oif, 

 and that it continued in some cases untd the leaf became 

 actually disintegrated, and long after all vitality appeared to 

 have departed. 



"It must, however, be borne in mind, that the circulation 

 in the lymphatic hairs of plants, in the chara and in the frogbit, 

 undoubtedly went on during life, and that it ceased -with the 

 death of the plant and the loss of vitality in the cell. 



"The author has repeatedly dried portions of the leaf of 

 the vabsneria, the chara, and frogbit, in which the circulation 



