408 MORPHOLOGY OF THE ANGIOSPERMS 



form two related, but distinct, families isolated in the loose, ranalian 

 complex. 



AUSTROBAILEYACEAE 



Austrobaileija, a genus described in 1929, is a woody vine, native in 

 northern Queensland. Because sufficient material was not available, its 

 taxonomic position was at first uncertain; it was suggested by some 

 taxonomists that it be placed in the Magnoliaceae; by others, in the 

 Dilleniaceae; and by still others, in the Monimiaceae. Additional collec- 

 tions and critical study have shown that it deserves family rank among 

 the more primitive Ranales. 



The simple leaves are pinnately veined. Their traces are two, derived 

 from the sides of a single gap (Fig. 5), the nodal structure now gen- 

 erally believed to be primitive for angiosperms. The perianth, con- 

 sisting of several free tepals, is not differentiated into calyx and corolla. 

 The stamens are laminar, with four median, protuberant, adaxial spo- 

 rangia ( Fig. 50 ) . Above the stamens are several staminodia, some transi- 

 tional to stamens. The several carpels are differentiated into ovary, 

 style, stigma, and a stout stipe. All the floral appendages are borne in 

 flattened spirals. The pollen is monocolpate, the ovules anatropous. The 

 bracts, tepals, and stamens have two vascular traces; the stamens and 

 staminodia show forms transitional to double and single traces. In the 

 carpels, the median bundle is double at the base, where two inde- 

 pendent traces unite. 



The cambium is primitive, with long-overlapping fusiform initials. Its 

 fairly primitive wood is unusual for a woody vine; its vessels are scalari- 

 form, with numerous perforations, and its tracheary pits are trans- 

 versely elongate. The phloem is remarkable for absence of companion 

 cells (Fig. 26). (The presence of companion cells in the phloem is 

 an outstanding angiosperm character, contrasting with the absence of 

 these cells in the phloem of gymnosperms. ) The phloem is primitive 

 also in its histological simplicity; it lacks sclerenchyma and typical 

 sieve tubes. The sieve elements are long-overlapping cefls, without 

 the specialized terminal sieve plates characteristic of true sieve tubes. 

 This simple phloem parallels in primitiveness the vesselless xylem of 

 other families. Retention of this primitive vascular structure in this 

 genus, a woody vine, is remarkable, because vines commonly have 

 highly specialized xylem and phloem. It is further remarkable that, as a 

 vine, it retains the most primitive nodal structure, not only at leafy 

 nodes but in the floral nodes, those of bract, tepal, stamen, and carpel. 



CERCroiPHYLLACEAE 



Among primitive dicotyledons, CercidiphyUiim, like Euptelea, has 

 long been of doubtful position; it has been considered a member of 



