214 THE INFLORESCENCE. 



393. The base both of the head and the umbel is frequently fur- 

 nished with a number of imperfect leaves or bracts, crowded into a 



cluster or whorl, termed an Involucre. The involucre assumes a 

 great variety of forms ; sometimes resembling a calyx ; and some- 



FIG. 320. Head of flowers of the Button-bush, Cephalanthus occidentalis. 

 FIG 321 Plant of Cornus Canadensis, with its four-leaved iuvolucre around a cluster of Email 

 owers. 322. A separate flower enlarged. 

 FIG. 323 Flowering branch of Cichory, with two heads of ligulate flowers. 



