IQlOl 



MILLER^LVCAS MEDIA 



211 



eter of 5.8 cm. There is practically no tapering to the columnar 

 trunk excepting at the very apex, while the pith actually increases 

 in diameter as it nears the apex, until it finally merges into the 

 plerome cylinder (fig. i). 



At the base of the stem there are 3 separate and distinct 

 vascular cylinders, the normal one nearest the pith and the 2 corti- 

 cal ones developed concen- 

 trically about the normal. 

 In previous accounts the 

 first cortical cylinder has 

 been reported to have a 

 development of xylem and 

 phloem equal to that of the 

 normal cylinder, while the 

 second and succeeding cor- 

 tical cylinders diminish 

 successiveh' in that devel- 

 opment toward the periph- 

 ery of the stem. 1 find in 

 this stem, however, that, 

 near the base, the first cor- 

 tical cylinder has a greater 

 radial extent of xylem and 

 phloem than has the nor- 

 mal one, while the second 

 is about the equal of 

 the normal, thus beginning 

 the successive decrease of 

 xylem and phloem develop- 

 ment which would likely 



be continued further if other vascular cylinders were present (fig. 2). 

 In each cylinder the xylem elements are of greater radial extent 

 than phloem elements, the former occupying approximately three- 

 fifths of the radial extent of the entire cylinder. 



At the stem apex only 2 vascular cylinders are evident (fig. 3). 

 Here the normal cylinder is seen to have xylem and phloem of 

 slightlv less radial extent than it has near the stem base, while 



//; 



Fig. I. — Cycas media: showing radial and 

 transverse aspects of polyxylic stem near tip; 

 »?, pith; p, plerome; .r, xylem; ph, phloem; c, 

 cortex. 



