106 PROCESS OF NUTRITION. CHAP. III. 



the evidence of experiment, would have seemed 

 altogether incredible. 



The sap then in ascending from the lower to the 

 upper extremity of the plant is propelled with a 

 very considerable force, at least in the bleeding 

 season. But is the ascending sap propelled indis- 

 criminately throughout the whole of the tubular 

 apparatus, or is it confined, in its course, to any 

 particular channel ? Before the anatomy of plants 

 had been studied with much accuracy, there was 

 a considerable diversity of opinion on the subject. 

 Channel Some thought it ascended by the bark ; others 



of ascent. 



thought it ascended by the bark, wood, and pith, 

 indiscriminately ; and others thought it ascended 

 between the bark and wood. 



According The first opinion was maintained and supported 

 pighi. by Malpighi ; who seems to have taken it for 

 granted that the sap ascends by the bark, merely 

 because the fibres of the bark (which he describes 

 under the appellation of Jibrce lignea, seu vasa 

 tubulosa)* had been found to be tubular, and 

 hence permeable to fluids : but this is a very lame 

 argument indeed ; for although the bark is of 

 a vascular texture and permeable to fluids, yet 

 this is no proof that the sap in its natural course 

 ascends through it, because the vessels contained 

 in it may possibly be destined for purposes very 

 different from that of the transmission of the 

 sap. But it was said that when a horizontal in- 



Anat. Plant, v. 

 fi 



