4.20 HYPERTROPHY. 
the ‘‘uovoli of the olive” and the ‘‘ burrs” that are 
formed on some varieties of apple, from which both 
roots and leaf-shoots are produced in abundance. 
A distinction must. be drawn between those instances 
in which the swelling is solid throughout from the 
excessive formation of cellular tissue, and those wherein 
it is hollow from the more rapid growth of the outer 
as contrasted with the mner portions. These latter 
cases might be classed under the head of distension. 
Enlargement of the buds may be seen in the case of 
bulbs and tubers. Occasionally these organs are 
developed in the axils of leaves, when their nature 

Fie. 201.—Formation of tubers or hypertrophied buds in the anil of 
leaves in the potato. 
