Boodle . — A natomy of the Gleicheniaceae . 717 
shaped, as described by Poirault. The points of agreement 
with the Eugleichenia- type are best seen in the species of 
smaller stature, e. g. in G. simplex , where the petiolar bundle 
is rather smaller than that of G. circinata. The xylem 
here has the form of an arch with sharply hooked ends, 
has a median and two lateral protoxylems in the usual 
positions ; the phloem is continued on the inner side of the 
xylem to about the same level as in G, dicarpa , and its 
elements are fibrous in the concavities of the xylem-hooks. 
A point of difference from the other subgenus is seen in 
the incurving of the endodermis, which may be described 
as having been pushed into the arched bundle by a pro- 
montory of cortical sclerenchyma. Other points of difference 
from Eugleichenia which would apply to a fair proportion 
of the species, are that in Mertensia the xylem-arch is com- 
posed of a continuous zone of tracheides of fairly uniform 
size, not interrupted by considerably smaller tracheides 
opposite the protoxylem-groups, and secondly that there is 
often a conspicuous group of small tracheides between the 
median protoxylem and the large tracheides forming the top 
of the xylem-arch. 
In species of Mertensia , where the petiolar bundle is larger 
than in G. simplex , the protoxylem-groups become more 
and more numerous according to the size of the xylem-arch. 
Thus both the median and the two lateral protoxylems may 
each be represented by two groups, making six in all, or, 
to take an extreme case, in a large form of G. longissima 
about twenty groups were counted. The leaf-trace in the 
upper part of Fig. 27 shows the form of petiolar bundle 
found in some of the larger Mertensias . 
The structure of the petiole of G. dichotoma differs from 
that of other species of Mertensia in that the bundle is 
bounded externally by an endodermis, which is not incurved, 
but in the central tissue of the bundle is found a mass of 
sclerotic tissue surrounded by a complete ring of endodermis 1 
1 Something similar to this is found in the basal part of the petiole of some 
Eugleichenias, to be described late’r, in dealing with the node. 
