Comparative Anatomy of the Casuarineae. 249 
three of them of parenchyma, these alternating the one with 
the other ; half of the whole circumference of the root was 
thus taken up by the three broad medullary rays, whose cells 
were thin-walled, more or less elongated radially, and densely 
packed with starch-grains. 
Remarks on the Structure of the Stem of Gnetum 
and Ephedra. 
As the Gnetaceae are regarded as the highest of the 
Gymnosperms, Gnetum and Ephedra were examined for 
comparison with Casuarina. 
Some structural points in Gnetum and Ephedra are of 
independent interest, and will therefore be described at some 
length. The species of Gnetum examined were — G. Gnemon , 
L., G. paniculatum, Benth., G. scandens , Roxb., G. neglectum , 
Blume, G. Thoa , R. Br. 
In these species the vessels formed next after the proto- 
xylem mostly have oblique end-walls with several round 
perforations or a single, long, narrow one. The later-formed 
vessels differ in having a single round perforation in each 
terminal wall. In the later vessels of G. Gnemon , most of 
the end-walls have a row of round perforations, while some 
have one long, narrow perforation, which would result from 
the fusion of several of the round ones (Fig. 31). Tracheides 
occur with a row of large, round-bordered pits on the terminal 
walls, as in Ephedra. One vessel in G. scandens showed an 
extraordinary long, oblique end-wall with many round per- 
forations (Fig. 32). In Gnetum Thoa the first vessels after 
the protoxylem have one to two large (Fig. 35), or several 
round perforations. Gnetum paniculatum was the most in- 
teresting species examined, as the node differs considerably 
from the internode in structure ; the node agreeing with 
Ephedra in the perforation of the vessels, &c. In the inter- 
node the first-formed vessels have several round perforations 
(Fig. 36) ; the outer ones have a single perforation. In one 
