FLORIN: SYSTEMATICS Of THE GYMNOSPERMS 361 



phylls. The strobili are built up of an axis and spirally arranged, homologous 

 scales. Most of these are sterile, and either simple or forked into two lobes, 

 while the remainder are megasporophylls. In the older type, crnciately dicho- 

 tomized sporophylls arise from the axis, each carrying two terminal but pendu- 

 lous ovules. The younger type has four to one megasporophylls, each terminated 

 by a single, erect ovule. In addition, the latter type has nonfunctioning sporo- 

 phylls, each with an aborting megasporangium. The vascular bundle of the 

 megasporophyll branches into three, of which the sporangium receives one and 

 the two apical fusing lobes of the sporophyll forming the integument one each. 

 Finally, Florin (1936a) investigated the epidermal structure of parallel- 

 veined, cordaiteanlike leaves of mesozoie age, and found that they represented 

 ginkgophytes, conifers, bennettites, or forms of uncertain position, but in no 

 case the cordaites. He concluded that the cordaitcs are in all probability an ex- 

 clusively paleozoic group of gymnosperms. It seems probaljle that they were 

 derived, independently of the pteridosperms, from primitive vascular plants 

 of the general psilophyte type. 



GlNKGOALES 



Gunckel and Wetmore (1946) investigated the origin and development of 

 the cortex, pith, and procambium in Ginkgo, the subsequent development of pri- 

 mary xylem and phloem, and the relation of the primary vascular strands to 

 the organization of the shoots. They demonstrated a close relation between the 

 vascular organization and the appearance of foliar primordia on the vegetative 

 apex. Two acropetally developing procambial strands are already projected into 

 the region of a presumptive leaf primordium before this primordium appears. 

 Contrary to previous concepts, the tM'o traces of a leaf have independent origins. 

 The female organ of Ginkgo still attracted much attention (Mehra, 1939; Kar- 

 stens, 1945; Florin, 1949; Nozeran, 1949b; and others). It had variously been 

 considered an axillary inflorescence; an axillary flow^er; a modified megasporo- 

 phyll; a dichotomized placenta; the fertile lobe of a trophosporophyll ; and an 

 axillary sporangial truss bearing terminal ovules. The collar at the base of the 

 ovule had been interpreted as two fused prophylls of a flower, as the vestige of 

 a true aril, as a megasporophyll, and as an outgrowth on the sporophyll, and 

 the integument as the two fused segments of a perianth, as two fused mega- 

 sporophylls, as a single megasporophyll, or as the lamina or part of the lamina 

 of a megasporophyll. Florin, wlio compared Ginkgo with Trichopitys (cf. be- 

 low), concluded: The ovulate complex is not an inflorescence (compound strobi- 

 lus) ; there are no leaf like megasporophylls or bracts. It might be called a 

 primitive "flower" (simple strobilus or fertile short shoot). The ovulate ap- 

 pendages of its axis have the character of sporangiophores. The "flower" is thus 

 a wholly fertile, dichotomized sporangial truss (syntelome) bearing terminal 

 ovules without any relation to leaves. It corresponds to the female flowers of 

 the cordaites and early conifers, but is not placed in an inflorescence. In No- 

 zeran's opinion, however, the normal biovulate organ is a leaf, inserted on a 

 rudimentary secondary axis, while Gaussen (1944-1952) regarded it as com- 

 posed of a much-reduced axis carrying one single or two-to-several fused uni- 

 ovular petioles (carpellary leaves). 



