70 MORPHOLOGY OF THE ANGIOSPERMS 



dormant axillary buds of dwarfed lateral branches may develop flowers, 

 as in some legumes — Cercis. Cauliflory is frequent in tropical forests 

 but rare in temperate regions. It has been considered, under the durian 

 theory, a primitive character, but the morphological relation of the in- 

 florescences to the trunk or larger branches — often developed from 

 adventitious buds — does not support this view. Cauliflory has been 

 described as related to pollination or seed dissemination by bats and 

 birds. Evidence that pollination in the primitive angiosperms was by 

 insects seems well supported. 



On the basis of order of development of flowers within the cluster, 

 inflorescences are classified as determinate (ctjmose) and indeterminate 

 (racemose). In determinate inflorescences, development of the first 

 flower limits apical growth of the main axis of the inflorescence, and 

 sequence in development of the other flowers is basipetal; in indetermi- 

 nate inflorescences, the first flower is the lowest, and order of develop- 

 ment of the others is acropetal — the number of flowers is theoretically 

 unlimited. Basipetal order of development is often called centrifugal, 

 and acropetal development, centripetal. 



It is unsatisfactory to use the order of development of flowers as a 

 basis for distinguishing the major types of inflorescences, and it is mor- 

 phologically inaccurate. Many inflorescences are intermediate in type, 

 especially racemose forms that have a terminal flower, as in Clethra, 

 ]uglans, Digitalis, Convallwia, Campanula, Pyrola. That the line be- 

 tween determinate and indeterminate inflorescences is weak is shown by 

 the large, branched inflorescences, which are often mixed, partly de- 

 terminate, partly indeterminate. Some families — the Campanulaceae, 

 Violaceae — have a great variety of inflorescences. A single genus, for 

 example, Hybanthus, may have both determinate and indeterminate 

 inflorescences. 



Descriptions and morphological interpretations of all the many varia- 

 tions and modifications of the two major types of inflorescences are not 

 considered here; they are described in elementary textbooks. Some of 

 the variations and modifications that are not readily interpretable or 

 are partly obscured by connation or adnation are discussed below. 



In the determinate inflorescences, the simple basic type, the dichasium, 

 consists of a terminal flower, with other flowers terminal on two lateral 

 axes borne in the axfls of bracts below the terminal flower. A similar 

 inflorescence, with more than two lateral branches, is a pleiochasium; 

 one with only one lateral branch, a monochasium. All these are termed 

 cymes, although "cyme" is often used as synonynous with dichasium. 

 Different types of monochasia are formed by differences in the position 

 and sequence of the successive branchings; among these are the helicoid 

 and scorpioid cyme and the cincinnus. The morphological nature of 



