INDETERMINATE INFLORESCENCE. 



213 



determinate infloresence, with the primary axis elongated, and the 

 flowers destitute of pedicels or with only very short ones. Two 

 varieties of the spike have received independent names, viz. the 

 Spadix and the Ament. 



390. A Spadix is a fleshy spike enveloped by a large bract or mod- 

 ified leaf, called a Spathe, as in Calla palustris (Fig. 313), the 

 Indian Turnip (Fig. 314), and the Skunk Cabbage (Fig. 1205). 



391. An Ament, or Catkin, is merely that kind of spike with scaly 

 bracts borne by the Birch (Fig. 312), Poplar, Willow, and, as to one 

 of the two sorts of flowers, by the Oak, Walnut, and Hickory, which 

 are accordingly called amentaceous trees. Catkins usually fall off 

 in one piece, after flowering or fruiting, especially sterile catkins. 



392. The Head, or Capitulum, is a globular cluster of sessile flowers, 

 like that of Clover, the Button-Bush (Fig. 320), and the balls of the 

 Buttonwood or Plane-tree. It is a many-flowered centripetal in- 

 florescence, in which neither the primaiy axis *ior the secondary 

 axes are at all lengthened. We may view it either as an umbel 

 without any pedicels, or as a spike with a very short axis. Gen- 

 erally it is of the latter character, as is evident in a Clover-head, 

 where what was first a head frequently elongates into a spike as it 

 grows older. 



FIG. 313, 31i. Spadix of Calla and of Arum, with the epathe. 315. A raceme of Cherry. 

 317. A cyme. 318. Panicle of TVIeadow-Graas. 319. A corymb. 



