720 Boodle. — - Anatomy of the Gleicheniaceae . 
the petiole, and may be described as being due to the folding 
back of the hook until the bay of parenchyma disappears. 
This may be illustrated in G. dichotoma by comparing Figs. 9 
and 8. 
Gleichenia, node. 
Diagrams of series of sections through the node, illustrating 
the mode of separation of the leaf-trace, have been given by 
Poirault (’ 93 , p. 172 et seq.) for two species of Eugleichenia 
and one of Mertensia. Poirault’s description of these makes 
most of the features clear, but as the nodal structure is very 
interesting, and as one or two particulars appear to have 
escaped Poirault, two series of diagrams are given here 
(Figs. 14-25), viz. one series for Mertensia and one for 
Eugleichenia. In examining the separation of the leaf-trace 
in three or four nodes of G. dichotoma , it was found that 
several differences of detail occurred. Probably the same 
would be found to apply to other species also. 
Fig. 14 represents the internodal structure of G. [Mertensia) 
dichotoma . Here we may speak of three upper and three 
lower protoxylem groups, or of two median and four lateral. 
Figs. 15-19 are diagrams of a series of sections through one 
particular node, which will now be described. On approach- 
ing this node 1 , the upper median protoxylem travels towards, 
and then fuses with, one of the adjacent protoxylems, thus 
reducing the number of protoxylem-groups to five, which are 
placed as seen in Fig. 1 5. The protoxylem-group, A, is the 
one that has been formed by the fusion of two. In succeed- 
ing sections the protoxylem, B, multiplies its constituent 
tracheides, and then forks into two, the parenchyma adjacent 
to it having meanwhile increased in amount, so as to produce 
an island in the xylem, which may be called the ‘ nodal 
island,’ as seen in Fig. ] 6, where n.i. is the nodal island, and 
b. are the protoxylems produced by the splitting of B. In 
the next stage (Fig. 17) the upper of these has travelled 
1 This and other nodes described are explained by beginning below and going 
in the acropetal direction. 
