142 
A. G. Tansley . 
from the form found in the typical Mertensias,’ for it is impossible 
to suppose that an isolated endodermis shut up in sclerenchymatous 
tissue can have an actual function. Further the fact that the 
Eugleichenias compared with the Mertensias are xerophilous forms 
distinctly lends support to the theory of reduction as applied to 
this series. 
Fig. 40. Gleichenia flabellata. Transverse sections through stele of node. 
sc. p., sclerenchyma of pocket ; i. ph., internal phloem. 
G. pectinata, on the other hand, is best regarded as derived 
from the Mertensia-type by the evolution of a regular pith. The 
co-existence in some cases of the nodal island, or, as it is better 
called, the nodal pocket, with the ordinary pith in this species is a 
curious feature scarcely compatible with the derivation of the 
Mertensia -type by reduction from a normal solenostelic form. 
Platyzoma again, with its extreme xerophily and anomalous leaf- 
traces may almost certainly be regarded as reduced from the 
solenostelic type. 
We are therefore led to the conclusion that such a form as 
G. flabellata on the whole represents the most primitive type of the 
genus, and it is interesting to note that not only do the branching 
of the fronds and the form of the pinnules but also the large number 
of spores in the sporangium (Bower, ’99) tend to corroborate this 
view. 
The Lindsava-Type. 
The next type of Filicinean vascular structure, naturally 
connecting with the Mertensia-type as seen in Gleichenia flabellata, 
' This view was put forward by Boodle (’01 B). 
