222 CORDAITEAE [CH. 



ment of secondary cortical tissue causes the exfoliation of the 

 superficial bark. 



In the form and structure of the fertile shoots Cordaites parts 

 company with Agathis; the trees bore no cones in the ordinary 

 sense, but unisexual inflorescences — whether on one plant or on 

 different individuals is uncertain — were produced in the axils or 

 from a supra-axillary position as compound spikes or compact 

 racemes. Both the longer female shoots and the shorter and 

 more compact male branches are constructed on a similar plan. 

 The ovulate inflorescence may exceed 30 cm. in length (fig. 479) ; 

 a stout axis bears • two-ranked hnear bracts subtending short 

 lateral bud-like shoots with one or several sessile or stalked 

 ovules (fig. 480) between the sterile scales. The seeds are platy- 

 spermic and agree much more closely with those of Cycads and 

 Gingko than with the seeds of Conifers. The male inflorescence 

 is on a smaller scale, in habit not unUke the elongated male shoot 

 of Cephalotaxus pedunculata and some other Conifers ; each 

 bract subtends a small oval bud composed of imbricate scales 

 and highly modified microsporophylls borne singly or in clusters 

 (figs. 481, F ; 482). A microsporophyll consists of a comparatively 

 long pedicel bearing at its apex a few long microsporangia. The 

 term microsporophyll imphes a morphological interpretation 

 which is not accepted by all palaeobotanists, some of whom 

 prefer to regard the microsporangia as stamens or microsporo- 

 phylls reduced to their simplest terms and sessile on an elongated 

 flower-stalk. 



The stem agrees very closely in its more important features 

 with that of an Araucaria or an Agathis: the primary xylem 

 fotms the inner surface of the thick cylinder of secondary wood, 

 merging gradually into it as in recent Conifers; there are no 

 separate bundles of primary centripetal xylem. The medullary 

 rays are narrow: in other words the secondary xylem is of the 

 pycnoxyhc type. The pitting of the tracheids is Araucarian and, 

 as in Agathis, the leaf-traces arise .as twin-bundles. The pith 

 is larger than in the Araucarineae and more homogeneous in 

 structure; it shares with the pith of Juglans and some other 

 recent plants an almost constant tendency to assume a discoid 

 structure. Anatomically the leaves agree more closely in the 



