104 UVFLORESCENCK. 



cences, are centripetal, wliile 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, whfle the general inflorescence is 

 centripetal. 



296. Of centripetal inflorescence the principal varieties are, 

 the spilte, raceme, ament, spadix, coiymb, umbel, head, 

 panicle, and thyrse. 



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

 sile flowers ai-ranged 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. Tlie raceme 

 may be either erect, 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 cal^rx and corolla, and 

 fall ofi' together, all remainmg still comiected with the rachis. 

 Ex. Salix, Betula. 



300. The SPADIX is a spike Avith a fleshy racliis enveloped in 

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



301. The coRYME 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 ( Crataegus ). 



302. An umbel resembles the cor^^mb, but the pedicels are of 

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

 common peduncle. Ex. Asclepias, Ai-alia 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 pecuhar to the vast family of the 

 Composit£e, and is equivalent to the compound flowers of the 

 earlier botanists. 



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



