310 Bower . — Studies in the Phytogeny of the Filicales. 
the initial segmentation. Three different types of segmentation are illus- 
trated in Fig. 44, a , b, c . In c there is a relatively massive stalk, such 
as might be found in any of the related genera above described. But 
in b the whole sporangium is more attenuated, while at the very base of the 
stalk it consists of a single cell-row with transverse segmentation. In a 
this condition is still more pronounced, and doubtless the three sporangia of 
Fig. 44 would correspond roughly in stalk-structure to the three sections 
shown in Fig. 43. But the condition does not appear to be uniform 
throughout the length of the stalk of any given sporangium ; thus in 
Fig. 44 > the stalk would consist at its base of a single cell-row, and in its 
upper parts of two or even three rows. Examination of sporangia dis- 
sected out separately from a sorus show that this is actually the case, one 
or two of the cell-rows stopping short before the base of the stalk is reached. 
In fact, the condition is closely similar to that shown by Mullers drawings 
of Asplenium trichomanes , quoted by Engler u. Prantl, i, 4, p. 81, Fig. 57. 
The sporangium itself is of relatively small size. The annulus is 
indurated on one side of the sporangium right down to the insertion of 
the stalk, but there interrupted. On the other side is the stomium, com- 
posed of the usual group of four cells. Attached to the stalk of most 
sporangia is a hair, which often shows a glandular terminal head, similar 
to what is seen in Nephrodimn . This fact acquires greater point when it 
is remembered how like Hypoderris is in habit to Aspidium trifoliatum. 
The interest of the facts thus related for Hypoderris lies in the com- 
parison of like conditions in other Ferns. No one has doubted that the 
natural place of Hypoderris is with Woodsia , and in less near relation with 
other Ferns with a basal indusium. But it stands apart from them in its 
relatively disintegrated vascular system of stock and petiole ; its broad 
leaves with reticulate venation ; in its mixed sorus, and reduced type of 
sporangium. The progression has been parallel along these distinct lines of 
character, and the changes from type thus shown here in an isolated genus 
of a well-defined affinity are matched very closely by similar progressions in 
other types of Ferns believed to be phyletically distinct. The more 
frequently such parallel progressions are traced the greater is the confidence 
in believing them to be indications of true phyletic advance. But the ques- 
tion why they should run so strictly parallel remains awaiting its full 
physiological explanation. As to Hypoderris itself, it may be held to be 
a member of the Woodsia affinity, modified as a tropical shade-form. The 
broad reticulate leaf follows on this habit ; but not so clearly the disintegra- 
tion of the stele, or the mixed character of the sorus. The reduction seen 
in the sporangium is, however, to be related with the continued production 
of sporangia in the mixed sorus. 
