1919I MILLER— CYC AS MEDIA 213 



The cortex, true to cycadean character, is relatively large, as 

 well as the pith. At the stem base the cortex measures 2.9cm. 

 between the outermost cortical cylinder and the leaf base, and 

 at the tip 2 cm. A great many leaf traces traverse the cortex. 

 At the base of the stem these traces are seen in longitudinal sec- 

 tion (fig. 2), excepting at those places where they are just leaving 

 the vascular cylinder. At the tip, however, leaf traces are invari- 

 ably seen in transverse section (fig. 3), and they are character- 

 istically double where they are about to enter a leaf base. Traces 

 may leave any or all of the vascular cylinders, those from the 

 inner ones passing to the cortex through the medullary rays of 

 one or more outer cylinders. 



DETAILED STRUCTURE 



Normal cylinder. — Vascular bundles of the normal cylinder 

 are long and narrow in transverse section (fig. 4), rarely becoming 

 more than 3 or 4 cells in tangential thickness. Bundles taper to 

 a rather sharp point toward the pith, and there is located the 

 definite endarch protoxylem. Wordsell had difficulty in locat- 

 ing protoxylem in the stem of Macrozamia which he studied, for 

 it had been obliterated by the crushing caused by thickening wood 

 cells. In the specimen which I studied the protoxylem is still 

 intact in the majority of cases, and is easily distinguished (fig. 4). 

 Fig. 5 represents protoxylem of the normal cylinder, enlarged 

 enough to show its detailed character. The cell walls are less 

 thickened than those of the primary xylem above, and there are 

 certainly no pits present, as there would be if the xylem were of 

 secondary origin. In this particular instance pits are absent from 

 the primary xylem also. This is an unusual condition, since, as 

 in fig. 6, primary xylem of the normal cylinder is practically 

 always scalariform. Fig. 6 shows the radial aspect of the normal 

 cylinder in its centripetal region. Here protoxylem elements are 

 unquestionably spiral in character, while the succeeding primary 

 xylem is scalariform. It should be said here that spiral tracheids 

 are of comparatively rare occurrence even in the normal cylinder; 

 at least they are rare in stretches large enough to be correctly 

 interpreted. The usual form of protoxylem is scalariform rather 



