*37 
The Gleicheniacece and Lindsay ecc . 
with a layer of pericycle and endodermis, which follows the curve 
of the xylem both within and without. The phloem does not line 
the whole concavity of the xylem arch though it extends round the 
free ends. This is also the typical form of leaf-trace in solenostelic 
ferns, though in most cases the phloem completely lines the con¬ 
cavity of the xylem arch. In G. ( Mertensin ) linearis , which stands 
apart from the other Mertensias in more than one respect, the 
sclerenchyma in the concavity of the petiolar strand is completely 
enclosed by a separate internal endodermis not continuous with 
the external one, so that this sclerenchyma is quite shut off from 
the cortex (Fig. 35). This type of structure is intermediate 
between the Mertensin- and the Eugleichenia- types. 
Fig. 35. Gteichenia linearis. T. S. of petiolar strand, e, external endo¬ 
dermis ; i.e., internal endodermis ; sc., sclerenchyma. From Boodle. 
The petiolar strand of Eugleichenia somewhat resembles the 
commonest Hymenophyllaceous type, z.e., the outline of the endo¬ 
dermis is circular or oval in section, enclosing an arch-shaped, 
xylem with the free ends terminating in incurved hooks. The 
phloem however, unlike that of the Hymenophyllaceae, often passes 
in round the xylem hooks, and sometimes (e.g. in G. dicarpa) forms 
an almost complete lining to the xylem arch (Fig. 36). The central 
parenchyma of the petiolar bundle sometimes has a strand of 
sclerenchyma in its midst (Fig. 36), as in Trichomanes Prieurii. 
This is not bounded by an internal endodermis, as in G. linearis, 
but in the base of the petiole an isolated internal endodermis 
appears in some species (G. dicarpa Fig. 37D), G. circinata (Fig. 
38) enclosing a strand of sclerenchyma within the main sclerenchy- 
