86 INFLORESCENCE. [chap. 



of florets are arranged upon a conical or flattened disk (the 

 common receptacle) surrounded by an involucre. Such an 

 inflorescence may be called a flower-head. The older 

 l)otanists used to regard the flower-head as a kind of com- 

 pound flower, enclosed in a common calyx, but we found 

 in the Zinnia that it was composed of a number of distinct 

 flowers (florets), each with its own calyx and corolla. The 

 ring of bract-leaves which surrounds the flower-head answers 

 to the ring surrounding the umbel, and is called by the same 

 name — involucre. 



In the Poppy and Sacred Lotus the peduncle (scape) 

 terminates in a solitary flower. In Mustard we found that 

 the peduncle does not itself terminate in a flower, but gives 

 off" a succession of secondary branches (pedicels), each of 

 which bears a flower. If we take a Ranunculus, we shall 

 find that the main or primary stem of the plant directly 

 terminates in a flower like that of Poppy, and if, as is usual, 

 there is more than one flower upon the plant, the 2dj 3d, 

 4th flowers, and so on, terminate respectively as many 

 successive independent branches, springing from the axils 

 of the leaves. Such forms of inflorescence, in which the 

 peduncle, or axis, itself terminates in a flower, are termed 

 definite or cymose, while those inflorescences in which the 

 principal axis never actually terminates in a flower, but, as 

 in Mustard, gives off" a succession of lateral pedicels, are 

 termed indefinite. In the St. John's Worts {Hypericuni) and 

 Exacum we have the cymose or definite inflorescence well 

 shown in their characteristic, forked cymes. 



An inflorescence which branches irregularly, like that of 

 Melia, Litchi, Mango, and most Grasses, is called di panicle. 



In describing the form of an inflorescence, when it does 

 not exactly coincide with any of the principal types here 

 defined, that which is nearest may, for the present, be 



