74 



MORPHOLOGY OF THE ANGIOSPERMS 



of the inflorescence form a spherical cluster, with its many flowers com- 

 pacted on the fused branchlets (Fig. 32C). Within the genus, the 

 pistillate heads are reduced from a racemose series to one (Fig. 32E). 

 The surviving head appears terminal but is the proximal member of 

 the series. The phyllotactic spiral of the branchlets making up a head 

 can be seen indistinctly on the proximal surface of the head and is clear 

 anatomically. (The staminate heads are not reduced in number but are 

 ephemeral. ) 



The oaks {Quercus) show, in the acorn cups and acorns, a similar 

 reduction of the compacted pistillate clusters. The primitive pistillate 



D 



Fig. 32. Diagrams to show the evolution of the inflorescence of Platanus. A, B, 

 showing the fundamental racemose character of the inflorescence; C, inflorescence 

 with each lateral branch condensed, forming a head, the lateral branchlets retaining 

 in the head their phyllotactic position; C, D, E, a series showing reduction in 

 number of heads from five to one. (After Boothroijd.) 



inflorescence of this genus is a large complex panicle, one still present 

 in some tropical species. The ultimate cymose branchlet systems have 

 been reduced to fused woody "cups," surrounding a terminal flower 

 (Fig. 33A). The bracts of the fused branchlets form the scales of the 

 cup. In primitive living species, many acorns are borne laterally on 

 elongate branching axes; in temperate-climate oaks, the cups are re- 

 duced to a few, which are borne on shortened, rarely branching axes 

 (white oaks), and to two or one on a very short axis (black oaks). The 

 family Fagaceae shows also a series in reduction in number of flowers 

 within the surviving fertile cluster — Costanea has five or three flowers; 

 Fagiis, two (Fig. 33B); Quercus, one (Fig. 33A). The lepidocaryoid 

 palms show a similar reduction of the pistillate inflorescence, with the 

 union of the bracts of the sterile branchlets forming an "armored" 

 sheath, the lorica (Fig. 34). The lorica surrounds a surviving terminal 



