54 PLANTS 



This is the modification of a branch, involving both stem and 

 leaves, which results in the structure we call the flower. 



1 1 6. A leaf bud and a flower bud are in all essential points 

 alike. There is a very short central axis around which are 

 arranged the rudimentary leaves in regular whorled or spiral 

 order. In the development of the leaf bud the axis elongates, 

 separating the leaves, while the latter expand and assume the 

 form and color of the typical leaf. In the case of the flower 

 bud, however, the axis does not elongate regularly throughout 

 its length. It may remain very short, in which case the flower 

 remains sessile. If the axis elongates at all the elongation 

 affects only a limited part, by which a stem (pedicel or peduncle) 

 is formed. At the top of this stem the flower leaves still remain 

 in closely set whorls or circles. 



Inflorescence 



117. The homology of flowers is also shown by their position 

 on the stem and their groupings. When flowers occur singly 

 they are either terminal or axillary and hence arise from ter- 

 minal or axillary buds, or else they spring from accessory buds. 

 In either case their origin is the same as that of branches. 

 Whenever a flower terminates an axis the growth of that axis 

 ceases with the growth of the flower, consequently further 

 growth of the plant must proceed from another bud. 



118. Flowers which occur in groups may be divided into two 

 classes, depending upon whether the first flower to appear is 

 terminal or lateral. In the former the grouping of the flowers 

 is called a determinate or cymose inflorescence. In this case 

 the first terminal flower is followed by two opposite, lateral 

 ones which grow beyond the first, leaving it apparently in the 

 angle of two equal lateral branches. This is a simple cyme. 

 If the two lateral flower stalks also each put out, in a similar 

 way, a pair of lateral flowers, the cyme becomes compound. 



