L 216 ] 



la the summer of 1804, I examined some elms 

 at Kensington. The bark of many of them had been 

 very much injured, and in some cases more than a 

 square foot had been stripped off. In most of the 

 wounds the formation of the new cortical layers was 

 from above, and gradually extending downwards 

 round the aperture ; but in two instances there had 

 been very distinctly a formation of bark towards the 

 lower edge. I was at first very much surprised at 

 this appearance, so contradictory to the general 

 opinion ; but on passing the point of a pen-knife along 

 the surface of the alburnum, from below upwards, I 

 found that a part of the cortical layer, which was of 

 the colour of the alburnum, had remained communi- 

 cating with the upper edge of the wound, and that 

 the new bark had formed from this layer. I have had 

 no opportunity of looking at the trees lately j but I 

 doubt not that the phenomenon may still be observ- 

 ed ; for some years must elapse before the new forma- 

 tions will be complete. 



In accounting for the experiment of M. Palisot 

 de Beauvois, mentioned in the Third Lecture, it may 

 be supposed that the cortical fluid flowed down the 

 alburnum upon the insulated bark, and thus occasion- 

 ed its increase ; or it may be conceived that the bark 

 itself contained sufficient cortical fluid at the time of 

 its separation to form new parts by its action upon the 

 alburnous fluid. 



The motion of the sap through the bark seems 

 principally to depend upon gravitation. When the 

 watery particles have been considerably dissipated 



