26o DISEASE IN PLANTS. 



When, by the breaking of the branch above 

 the insertion of the dormant bud or by pruning, 

 defohation by insects, etc. the transpiration 

 current and supph'es of food materials are in any 

 way deflected to the minute cambium and growing 

 points of the dormant buds, they are stimulated 

 to normal growth, and may grow out as epicormic 

 shoots or " shoots from the old wood." In many 

 cases such epicormic shoots are stimulated to 

 grow out by suddenly exposing an old tree to 

 more favourable conditions of root-action and 

 assimilatory activity, owing to the felling of 

 competing trees which previously hemmed it in 

 from light and air, and restricted the spread and 

 action of its roots in the soil. This is often 

 seen in old Elms, Limes, etc. 



It is by such means as the above that substitu- 

 tion branches are obtained when a leader is 

 broken or cut away. 



Adventitious buds are such as are newly formed 

 from callus or other tissues in places not normally 

 provided with buds, a.s is often seen on occluding 

 wounds e.g. stool shoots. They may also be 

 developed on roots, a fact utilised in propagating 

 Bouvardias, Horse-radish, etc., by means of root- 

 cuttings, and the suckers of Plums and other fruit 

 trees are shoots springing from adventitious buds 

 on roots. 



Adventitious buds are also common on leaves 

 {e.g. Bryophylluvi, Ferns, etc.), and are frequently 

 induced on them by wounds e.g. Gesneria, 

 Gloxinia, etc. Even cut cotyledons may develop 



