C'EXTRll'UGAL INFLOKESCENCE. 



103 



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

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

 nists have recently observed two important distinctions, namely, 

 the centripetal and the centrifugal, the former resulting from 

 axillary, and the other from terminal flowers. 



293. Li CENTRIPETAL infloresccncc 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 Umbelliferae and the Cruciferce. 



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

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

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

 rachis, is lengthened, it is the centre which it beai's along with it at its apex, leav- 

 ing the circumference at the base. 



294. In CENTRIFUGAL inflorescencc the blossoming com- 

 mences with 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 first which 

 teiTninates the axis) temiinate lateral branches 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 tAvo modes of inflorescence 

 combined in the same plant. In the CompositEe, as Dr. Gray 

 remarks, the heads, which may be called the ^^(^rtial inflores- 



