340 CONSERVATIVE ORGANS. [LECT. VII. 



" several inches in length was made in the bark of 

 " a branch of Willow, three or four years old, and 

 " the bark loosened, so that it might be slipt 

 " aside from the wood in the form of a hollow 

 " cylinder, the two ends being undisturbed. The 

 " edges of the bark were then united as carefully 

 " as possible, the wood covered from the air, and 

 " the whole bound up to secure it from external 

 " injury. After a few years, the branch was cut 

 " through transversely. The cylinder of bark was 

 " found lined with layers of new wood, whose num- 

 " ber, added to those in the wood from which it 

 " had been stripped, made up the number of rings 

 " in the branch above and below the experi- 

 " ment *." But if these experiments do not prove 

 the truth of Malpighi's opinion, they completely 

 disprove the hypothesis of Hales; and throw great 

 light upon the fact, that the alburnum is actually 

 formed from the secretion deposited by the vessels 

 of the liber ; an opinion which has been fully es- 

 tablished by the experiments of Mr. Knight*)-. 



* Introduction to physiological and systematical Botany , 

 chap. iv. 



f It is but justice to say, that although Dr. Hales states it 

 as his opinion that " the new zone of wood is formed by the 

 " shooting of the longitudinal fibres lengthways under the bark, 

 " as young fibrous shoots of roots do in the solid earth ;'* yet 

 that he afterwards remarks, " we may observe that nature has 

 " taken great care to keep the parts between the bark and wood 



