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 Labiatas the partial inflorescences (verticilas- 

 ters, 309) are centrifugal, wliile 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 aiTanged along a common peduncle (racliis). 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 erect, as in Hyacinthus, Pyrola, or pendulous, as 

 in the currant and black cheriy. 



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

 ered each ^vith a scaly bract, instead of a cal^rx and corolla, and 

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

 Ex. Salix, Betula. 



300. The SPADIX is a spike A\dtli a fleshy rachis enveloped in 

 a large bract, called spathe. Ex. Ai-um, 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 (Cratccgus). 



302. An UMBEL resembles the coiymb, 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 

 Composita3, and is equivalent to the compound Jloivers of the 

 earlier botanists. 



h. In the capitulum there is a general resemblance to the simple flower, the 



