THE OAK. 



43 



as soon as they have shed their pollen, being no 

 longer of any use. Those stalks, however, to 

 which galls are attached, remain firmly united 

 with the tree, and grow vigorously as long as the 



FLOWER-GALLS. 



grubs contained in them continue to feed. The 

 notice of this circumstance has helped to decide 

 one of the controverted points in vegetable phy- 

 siology — namely, whether the sap is forced into 

 motion by some power residing within the tree, or 

 whether, being evaporated or otherwise consumed 

 at the extremities, a fresh supply rises to fill its 

 place. In favour of the latter supposition many 

 arguments may be adduced ; and, among them, 

 that furnished by the flower-stalks of the Oak, 

 which cease to receive sap, and wither away, as 

 soon as their proper vital functions are at an end ; 

 but if they bear swelling galls on their extremi- 

 ties, contribute their share of influence towards 

 the ascent of sap throughout the tree generally, 



