126 



VEGETABLE SAP. 

 Fig 3.9. 



\ 



their form being generally oblongly round, but in- 

 creasing downward much more rapidly than in any 

 other direction. (Fig. 40.) 



Fig. 40. 



A protuberance on an elm. 



When these protuberances are laid open, we find 

 them composed of either cambium on their first 

 appearance, or of ligneous material after they are 

 six months old ; and evidently dilatations of the vital 



