PLANT ORGANS AND ORGANISMS l8l 



plants of the same family. In the cyme the development is centri- 

 fugal, the central florets opening first, while in the corymb it is 

 centripetal, or from margin to center. 



PREFLORAT1ON 



Prefloration. By prefloration is meant the arrangement of the 

 tioral envelopes in the bud. It is to the flower bud what vernation is 

 to the leaf bud, the same descriptive terms being largely employed, 

 as convolute, involute, revolute, plicate, imbricate, etc. 



In addition to those already defined, the following are important. 



Vahate Prefloration, in which the margins meet but do not over- 

 lap. Of this variety the induplicate has its two margins rolled 

 inward as in Clematis. In the reduplicate they are turned outward, 

 as the sepals of Althaea. 



Vexillary, the variety shown in the corolla of the Pea, where the 

 two lower petals are overlapped by two lateral ones, and the four in 

 turn overlapped by the larger upper ones. 



Contorted, where one margin is invariably exterior and the other 

 interior, giving the bud a twisted appearance, as in the Oleander and 

 Phlox. 



THE FLOWER 



The flower is a shoot which has undergone a series of changes so as 

 to serve as a means for the propagation of the individual. 



A Typical or Complete Flower possesses four whorls of floral leaves 

 arranged upon a more or less shortened stem axis called a receptacle, 

 torus or thalamus. These whorls passing from periphery toward the 

 center are: calyx, composed of parts called sepals; corolla, composed 

 of parts termed petals; andrcecium, composed of parts called stamens 

 or microsporopylls; and gyn&cium, composed of one or more parts 

 termed carpels or megasporophylls. 



The stamens and carpels constitute the essential organs, and a 

 flower is said to be Perfect when these are present and functional. 



A Hermaphrodite flower is one which possesses both stamens and 

 carpels which may or may not be functionally active. In some cases 

 the stamens may alone be functional while in others the carpels 

 only may function. 



