Seward— On the genus Myeloxylon ( Brong .). 17 
spondence 1 . Other forms of Myeloxylon- bundles might be 
quoted which find striking parallels in Dioon edule , Ceratozamia , 
Cycas , &c. 
The fusion of two or more bundles in living Cycads has 
been referred to by Vetters 2 and also by De Bary 3 : in the 
fossil petioles similar instances of fusion are found. 
4. Hypoderm , sub epidermal parenchyma , &*c. 
In well-preserved examples of Myeloxylon , e. g. Fig. 41, . 
Plate V in Renault’s paper, there are a few layers of paren- 
chyma immediately below the epidermis. Similar subepi- 
dermal parenchyma occurs in Angiopteris , as some writers 
have pointed out ; but in petioles of Cycads it is also present. 
In many specimens of Myeloxylon this parenchyma has been 
destroyed, e. g. in Fig. 8, but in a small section, which occurs 
on the same slide as the larger Binney specimen, this tissue 
is clearly shown. The canals of recent Cycads and the fossil 
petioles are practically identical. 
The hypodermal tissue of Myeloxylon closely corresponds 
with that of Encephalartos horridus , Macrozamia Hopei , and 
other species. In some of Renault’s specimens we see groups 
of thick-walled fibres in the ground-tissue ; Schenk refers to 
the absence of such in recent Cycads, but, as De Bary has 
remarked, groups of thick-walled fibres occur in various 
Cycadean petioles. 
In the bundles of Cycads we find a few xylem-tracheids 
among the delicate phloem-elements (‘ bois centrifuge ’) ; these 
have not been detected in the fossil bundles, as Solms has 
already noted. 
These tracheids are always much smaller than the other 
elements of the xylem, and, even in recent specimens, cannot 
in all cases be readily seen ; it is not improbable that such 
might fail to be preserved, or, if preserved, to be distin- 
guished from the surrounding phloem. 
1 Similar bundles occur in Stangeria paradoxa, Zamia muricata , &c. 
2 Vetters, Die Blattstiele der Cycadeen (Inaug. Dissert., Leipzig, 1884). 
3 De Bary, Comparative Anatomy of the vegetative organs of the Phanerogams 
and Ferns, p. 337 (1884). 
C 
