Boodle . — • Anatomy of the Gleicheniaceae. 741 
Summary. 
1. Two chief types of stem-structure are found in the 
genus Gleickenia : (a) protostelic, (b) solenostelic. The 
latter has only been met with in one species, G. pectinata. 
The genus Platyzoma exhibits a third type: (c) medullate 
stele, with annular xylem and internal endodermis. 
2 . The xylem is mesarch with distinct groups of spiral proto- 
xylem except in G . moniliformis and in Platyzoma . No spiral 
protoxylem was recognized in either of these, but in Platyzoma 
some of the smaller, sub-peripheral, or peripheral scalariform 
tracheides quite possibly represent scattered protoxylem. 
3. As pointed out by Poirault, the bundle of the petiole 
is rounded in Eugleichenia , and nearly always arched in 
Mertensia , but G. dichotoma forms an exception. General 
sclerosis of the pericycle in the petiole may occur in both 
subgenera. 
4. In all cases a single leaf-trace enters the petiole, and 
usually divides into three, close below the first pinnae ; in 
one species this division takes place near the base of the 
petiole. 
5. The xylem in the petiole has usually the form of an 
arch with incurved ends. Where the bundle is small, there 
are one median and two lateral protoxylems on the upper 
side of the xylem. In larger bundles the protoxylems are 
more numerous. 
6. In several species, at any rate, a nodal island is found 
in the xylem of the stele, as described by Poirault. It 
contains phloem and sclerenchyma ; the latter being sur- 
rounded by an endodermis. When the leaf-trace becomes 
free, the sclerotic tissue in the nodal island may fuse per- 
manently with the cortex, or it may have a transitory con- 
nexion with it, and then be continued for some distance 
upwards (surrounded by its endodermis) inside the petiolar 
bundle ; or it may have no connexion with the cortex, 
although continued to the top of the petiole inside the bundle 
(G. dichotoma). The phloem in the nodal island is connected 
3 C 2 
