296 Bower . — - Studies in the Phytogeny of the Filicales. 
emergences about the leaf-bases justifies the comparison of the branched 
hairs which they bear with the broad scales of the Cyatheaceae. Similar 
emergences also exist in Lophosoria (PL XXXI, Fig. G). The pro- 
gression of characters from the Gleicheniaceae to the Cyatheaceae through 
Lophosoria is in this case based upon a minor detail ; but the existence 
of such a detailed progression supports all the more strongly the comparisons 
based upon more important characters. 
4. By a general consensus of opinion the non-medullated stele is 
recognized as the primitive stelar type. The characteristic elaboration of 
this in Leptosporangiate Ferns was connected with the formation of foliar 
pockets, which intruded above the insertion of each leaf. This led to 
complete solenostely, with leaf-gaps. When the latter overlap one another 
the complete dictyostele is the result. No better illustration of these 
successive steps is to be found than in the Ferns under consideration. 
The sequence of stages of the elaboration is as follows ; In Gleichenia in 
general the stele of the rhizome has a solid xylem-core ; it is a protostele, 
from which the leaf-traces come off in some cases without any disturbance 
of the underlying tissues. The types of the genus described fall into 
a rough series, as regards their vascular characters, extending from the 
simple forms of Eu-Gleichenia , through G. linearis , to the typical Mertensias, 
and finally to G . pectinata (Tansley, ‘Lectures,’ p. 44). There is, however, 
reason to think that the first named owe their simplicity of structure to 
reduction in connexion with their xerophilous habit, and that G. flabellata 
may be regarded as a central and primitive example. It has a solid 
protostele, which gives off to each leaf a C-shaped trace, with a pocket of 
internal phloem, endodermis, and sclerenchyma, which is continued into the 
stele, but does not intrude far. G. pectinata is, however, a solenostelic form, 
which shows certain complications noted by Boodle and Hiley (‘Ann. ofBot.’, 
xxiii, p. 419). From the known facts it seems still uncertain what the 
exact steps were which led to the solenostelic structure there presented. 
This, however, is not the present question. What interests us is that, 
however produced, the solenostely exists in G. pectinata with a centrally 
placed sclerenchymatous pith, surrounded by endodermis and internal 
phloem. The internodes are long, so that the solenostelic structure is only 
interrupted by leaf-gaps at long intervals. Passing to Lophosoria the 
solenostelic structure is essentially the same as in G. pectinata , but the 
whole axis is on a more bulky scale. Though in the young plant of 
Lophosoria the sclerenchyma within the solenostele is at first solid, as in 
G . pectinata , in the older plant a parenchymatous core replaces the 
central region of that sclerenchyma, the remainder of which appears as 
a dark shell lining the solenostele internally, as is usual in the Cyatheaceae. 
The latter shows the usual amphiphloic structure, but there is no marked 
protoxylem : in this it differs from G, pectinata , but it shows a condition 
