BRANCHING OF STEMS 



41 



such a stem is definite in growth. AVhen lateral branches arise 

 upon it, they are generally few in number, and soon equal or 

 exceed the main stem in vigour. Branching of stems of definite 

 growth is said to be cymose ; it often resembles the diagrammatic 

 sketch b, Fig. 15. Cymose branching, however, sometimes 

 leads to the formation of what at first sight appears to be a 

 simple main axis of indefinite growth, but which is in reality 

 composed of a series of short axes of different orders. At 

 c. Fig. 15 is a main or primary axis i, which ends at x, its 

 growing point having developed a flower or been destroyed 

 by frost, wind, insect attacks or other means, and elongation 



Fig. 15.— Diagrams illustrating (a) indeBnite growth of stem, 

 and racemose branching ; (^) and (c) definite growth of stem and 

 cymose branching, i, 2, 3, axes of first, second, and third order ^ 

 respectively. 



thereby prevented. Below its tips a lateral bud has pro- 

 duced the branch or secondary axis 2 : the latter axis soon 

 ceased growth, and a branch of the third order, 3, was pro- 

 duced, a further one, 4, being developed in a similar manner. 

 The whole shoot from A to B, although crooked at first, may 

 ultimately straighten and appear similar to a simple single axis 

 of the first order of indefinite growth : when this happens such 

 a stem is termed a false main-axis or sympodium. 



The branches of elm, hazel, and many other trees which 



