104 INFLORESCENCE. 



cences, are centripetal, while the general inflorescence is centri- 

 fugal, that is, the central head is developed before the lateral 

 ones. But in the Labiates the partial inflorescences (verticilas- 

 .ters, 309) are centrifugal, while the general inflorescence is 

 centripetal. 



296. Of centripetal inflorescence the principal varieties are, 

 the spike, raceme, ament, spadix, corymb, umbel, head, 

 panicle, and thyrse. 



297. The SPIKE is an inflorescence consisting of several ses- 

 sile flowers arranged along a common peduncle (rachis). Ex. 

 Plantago, Verbascum. 



298. The RACEME is the same as the spike, but having the 

 flowers raised on pedicels, each being axillary to a bract, and 

 blossoming in succession from the base upwards. The raceme 

 may be either erecj, as in Hyacinthus, Pyrola, or pendulous, as 

 in the currant and black cherry. 



299. The AMENT, or catkin, is a spike whose flowers are cov- 

 ered each with a scaly bract, instead of a calyx and corolla, and 

 fall off together, all remaining still connected with the rachis. 

 Ex. Salix, Betula. 



300. The SPADIX is a spike with a fleshy rachis enveloped in 

 a large bract, called spathe. Ex. Aram, Calla. 



301. The CORYMB is the same . as the raceme, having the 

 lower pedicels so lengthened as to elevate all the flowers to 

 nearly or quite the same level. Ex. wild thorn (Cratasgus). 



302. An UMBEL resembles the corymb, but the pedicels are of 

 nearly equal length, and- all arise from the same point in the 

 common peduncle. Ex. Asclepias, Aralia hispida, 'onion. 



303. A HEAD or CAPITULUM is similar to an umbel, but the 

 flowers are sessile or nearly so upon the summit of the pedun- 

 cle. Ex. button-bush, clover, globe-amaranth (Gomphrena). 



a. But the more common kind of capitulum is that where the 

 summit of the peduncle (rachis) is dilated into a broad disk (re- 

 ceptacle) bearing the sessile flowers upon its surface. This is 

 the kind of inflorescence peculiar to the vast family of the 

 Compositae, and is equivalent to the compound flowers of the 

 earlier botanists. 



b. In the rtipttulum there is a general resemblance to the simple flower, the 



