138 BOTANY AND PHARMACOGNOSY. 



the pedicels of the flowers are so elongated that all of the flowers 

 attain nearly the same height or level, this form of inflorescence 

 being known as a corymb ; in the milk weed the rachis is entirely 

 suppressed and the flowers, which have pedicels of the same 

 length, arise from the apex of the peduncle, this form of inflor- 

 escence being known as an umbel- (Fig. 173) ; in the Umbelliferae 

 a flower cluster takes the place of the individual flowers of the 

 umbel, and this is known as a compound umbel (Figs. 169, 170) ; 

 in the plantain the flowers are arranged along a central axis, but 

 the pedicels are wanting, and the inflorescence is known as a 

 SPIKE (Fig. 87, illus. 3) ; in clover, Cephalwnthns and the Com- 

 positse, the rachis and pedicels are both more or less reduced, 

 or wanting, and this form of inflorescence is known as a head 

 (Figs. 181, 182). 



The DETERMINATE or DEFINITE INFLORESCENCE includes Sev- 

 eral types, the principal of which may be mentioned : when a stem 

 or branch is terminated by a flower, or a cluster of flowers 

 of the determinate type, it is known as a cyme, and an inflor- 

 escence of this character is described as cymose ; when the pedun- 

 cle bears a number of cymes, it is known as a compound 

 CYME, as in elder, hydrangea and viburnum ; and a cymose head 

 is known as a glomerule, as in the dogwood. When the cymes 

 are opposite and sessile, or nearly so, the inflorescence is termed a 

 verticillaster, as in the Labiatse. 



The flowers of the Compositce are borne on a common torus 

 known as the disk, which is subtended by one or more circles of 

 bracts, these constituting an involucre. The flowers are of two 

 kinds, and they receive different names because of their form and 

 position. Those situated near the margin of the disk are known 

 as RAY-FLOWERS, and because they possess more or less strap- 

 shaped corollas are also known as ligulate flowers. Those 

 occupying the central portion of the disk are known as disk- 

 flowers, or as tubular flowers because of the tubular shape of 

 the corolla. Most of the Compositse possess both ligulate and 

 tubular flowers, as Arnica (Fig. 241), matricaria, the common 

 daisy, etc. But some of the members of the family have only 

 ligulate flowers, as chicory and dandelion; and a relatively few 

 have only tubular flowers. 



