117, 118.] INFLORESCENCE. 137 



351. The forms of inflorescence are exceedingly 

 various, but may all be referred to two classes, as 

 already indicated the axillary, in which all the 

 flowers arise from axillary buds ; the terminal, in 

 which all the flower-buds are terminal. 



352. Axillary inflorescence is called indefinite, be- 

 cause the axis, being terminated by a leaf-bud, con- 

 tinues to grow on indefinitely, developing bracts with 

 their axillary flowers as it grows. It is also called 

 centripetal, because in the order of time the blossom- 

 ing commences with the circumference (or base) of 

 the inflorescence, and proceeds toward the central or 

 terminal bud, as in Hawthorn or Mustard. 



353. Terminal inflorescence is definite, implying 

 that the growth of the axis as well as of each branch 

 is definitely arrested by a flower. It is also centrifu- 

 gal, because the blossoming commences with the cen- 

 tral flower and proceeds in order to the circumference, 

 as in the Sweet- William, Elder, Hydrangea. 



354. Both kinds of inflorescence are occasionally combined in the same 

 plant, where the general system may be -distinguished from the partial clusters 

 which compose it. Thus in the Compositae, while the florets of each head 

 open centripetally, the general inflorescence is centrifugal, that is, the termi- 

 nal head is developed before the lateral ones. But in the Labiatee the partial 

 clusters (verticillasters) open centrifugally, while the general inflorescence is 

 indefinite, proceeding from the base upward. 



CHAPTER 



SPECIAL FORMS OF INFLORESCENCE. 



355. Of centripetal or axillary inflorescence the 



principal varieties are : the spike, spadix, catkin, raceme, 

 corymb, umbel, panicle, thyrse, and head. The spike 

 is a long rachis with sessile flowers either scattered, 



