CENTRIFUGAL INFLOllESCENCE. 



103 



292. In regard to the evolution of the inflorescence, that is, 

 the mode of succession in tlie development of the flowers, bota- 

 nists have recently observed two important distinctions, namely, 

 the centripetal and the centrifugal^ the former rcsidting from 

 axillary, and the other from terminal flowers. 



293. In CENTRIPETAL infloresceiice the evolution (blossoming) 

 of the flowers commences with those of the circumference (or 

 the base) and proceeds towards the centre (or the summit), as 

 in the Umbellifera3 and the Cruciferte. 



a. The student will readily perceive that the circumference of a depressed (flat- 

 tened, inflorescence corresponds to the base of a lengthened one; and also that the 

 centre of the foiTner answers to the summit of the latter. For when the axis, or 

 rachis, is lengthened, it is the centre which it bears along with it at its apex, leav- 

 ing the circumference at the base. 



294. In CENTRIFUGAL inflorcsceuce the blossoming com- 

 mences ^\dth the terminal and central flower, and proceeds 

 towards the lateral flowers, or those of the circumference. Ex. 

 Hydrangea, elder, and the pink tribe. 



a. ' This mode of inflorescence is generally indicated by the presence of a soli- 

 tary flower seated in the axils of the dichotomous (forked) branches.' All the 

 flowers are considered terminal, because they do in fact (except the fii-st which 

 terminates the axis) terminate /a^eraZ feranc^es successively produced at the node 

 next below the primary flower. This is beautifully illustrated in Spergula. 



FIG. 37. — Modes of inflorescence ; 1, centrifugal inflorescence (cyme) of Cerastium maxi- 

 mum ; 2, fascicle ; 3, centripetal inflorescence (corymb) ; 4, spike. 



295. Sometimes we find these two modes of inflorescence 

 combined in the same plant. Li the CompositEP, as Dr. Gray 

 remarks, the heads, which may be called the partial inflores- 



