222 COBDAITEAE [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 linear 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 unlike 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 implies 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 

 forms 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 

 pycnoxylic 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 



