68 



MORPHOLOGY OF THE ANGIOSPERMS 



grass trees, Xanthorrhoea (Fig. 29), similarly have millions of flowers 

 in a contracted panicle of cylindrical form, which may be 2 m long. 

 The inflorescence of Tijpha has been estimated to bear 300,000 flowers. 

 Most inflorescences die as soon as the fruit is mature, and many are 

 soon abscised; rarely, they are biennial or perennial, with annual or 

 continuous flowering. Those of some Bromeliaceae produce flowers for 

 two or three seasons, and those of Couroupida, the cannonball tree, 



A ^ B 



Fig. 28. Sketch of inflorescence of Galinsoga simulating a flower. A, face view show- 

 ing ray and disc flowers; B, lateral view showing subtending bracts. {Drawing by 

 Elfriede Abbe. ) 



persist on the tree trunk for many years, leafless but woody, and in- 

 crease in length and diameter like vegetative branches. 



Classification 



Many descriptive terms have been applied to the varieties of in- 

 florescences, terms the use and meaning of which have often been loose; 

 transitional types are common and rigid definition cannot be made. 

 Inflorescences have been classified on two bases: that of position on 

 the stem system, and that of sequence in flowering within the cluster. 



On the basis of position on the stem, they are grouped as terminal, 

 axillary, and intercalary. Strictly terminal clusters terminate branches; 

 axillary clusters are terminal on short axillary branches or represent 

 foliaceous axillary branches which have been reduced to inflorescences; 

 intercalary inflorescences are terminal clusters that have been "left be- 

 hind" by continuing apical growth of the main axis, which forms, alter- 

 nately, fertile and sterile sections, or by sympodial growth. Myrtaceous 

 genera, such as Callistemon, the bottle brush, and Melaleuca, the paper- 

 bark tree, are excellent examples of the intercalary type. Inflorescences 



