THE FLOWER 87 



The looseness of use of the term flower by botanists is, in part, re- 

 sponsible for the difficulty in defining the structure. By "the flowering 

 plants" is commonly meant the angiosperms, but such phrases as "the 

 flowering of the conifers" (referring to the period of pollination), "the 

 flowers of the gymnosperms," and "the flowers of the seed plants" are 

 frequently seen. 



Basic Structure 



The Receptacle. The flower is, first of all, a stem tip, the receptacle, 

 resembling in ontogeny and fundamental structure a vegetative tip. It 

 consists of nodes and internodes and bears appendages. The nodes are 

 usually closely crowded by shortening and often brought together by 

 suppression of internodes. Apical growth is limited early in develop- 

 ment, but other growth may continue until the fruit is mature. That 

 the flower is only in part a mature structure is commonly overlooked; 

 the receptacle and carpels are still in early stages when the rest of the 

 flower is mature. (Failure to recognize that the vascular supply of the 

 carpels within the receptacle is incomplete at flowering time has led to 

 incorrect interpretations of the nature of the flower and its parts.) The 

 receptacle is often greatly modified and unstemlike in form, size, and 

 structure; and, as it matures with the fruit, it may become still less 

 stemlike. 



On the receptacle are borne, typically, both fertile and sterile ap- 

 pendages. The shortening and suppression of internodes bring the ap- 

 pendages close together, either in spirals or whorls. Whorls repre- 

 sent the more specialized arrangement, as in leaf arrangement; a 

 whorl represents one or more "turns" of a flattened spiral. Parts of 

 highly compressed spirals often pass as whorls, as they appear to be 

 from naked-eye and hand-lens inspection (and are, for practical pur- 

 poses, in taxonomic description), but they can be seen to be spiral by 

 anatomical study. Each organ stands at a level microscopically different 

 from the others, as in the corolla of Ranunciihis. The appendages may 

 all stand in spirals or all in whorls, or part may be spirally placed and 

 part in whorls. Where all types are spiral, the spiral may run con- 

 tinuously throughout the flower, as in Poeonia; more often, there are 

 discontinuities iDctween the different kinds of organs. Where the ap- 

 pendages are all in whorls, the members of successive whorls usually 

 alternate in position with those of the whorls directly above and be- 

 low; where there are several or many whorls of organs of one kind, as 

 in the androecium of Aqidlegia, the organs may stand in longitudinal 

 rows. Typically, the different kinds of organs — though separated by 

 breaks in phyllotactic continuity — stand close to one another longi- 

 tudinally on the receptacle, but there may be prominent, naked inter- 



