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MR. F. 0. BOWER OX THE COMPARATIVE MORPHOLOGY OF THE 
to this tiiat the branched leaf has so long been treated as one member, and not as a 
branch-system. Differences of localisation of intercalary growth are regarded as of but 
secondary importance in the morphology of axes, and they should be regarded in the 
same light in the morphology of leaves : the neglect of this principle has resulted in 
the division of the primordial leaf into the foliar base (blattgrund) and upper leaf 
(oberblatt), two categories which, as I have pointed out in the introduction to this 
essay, are not morphologically co-ordinate in the case of branched leaves. 
With the more complete differentiation of the phyllopodium and the pinnse there 
appears also a differentiation of the parts of the phyllopodium itself, corresponding to 
and foreshadowing that more complete differentiation which is found among the 
higher vascular plants. There, as above pointed out, three parts of the phyllopodium 
may be distinguished : the hypopodium which coincides with Eichler’s “ blattgrund 
the mesopodium or petiole ; and the epipodium, which includes the upper part of the 
phyllopodium with its wings, but exclusive of its branches of higher order. That 
these are parts only of one podium, and not fundamentally different parts, as Eichlf.r 
would have it ( l.c ., p. 25), appears to me to be strongly supported by a comparative 
study of the leaves in the series of plants above treated in detail. As I have 
repeatedly pointed out, the phyllopodium is fundamentally a winged structure 
throughout its length, though the wings are not uniformly developed, and are 
sometimes partially or entirely (Pilularia) suppressed. In the plants of this series 
which have the simplest structure ( Hymenophyllacece ) the different parts of the 
phyllopodium are not distinguishable : its development is almost uniform throughout. 
In the majority of the Leptosporangiate Ferns their differentiation is but slight, 
though in some forms—for instance, Aspidium Filix-Mas and Onoclea germanica — a 
somewhat distended basal portion may be distinguished from the upper parts of the 
phyllopodium. In Osmunda the distinction of the basal part or hypopodium is more 
marked, the lateral wings being more bulky and extended ; in Todea the winged 
development is not exclusively lateral, but is continued transversely across the face 
of the phyllopodium, so as to form a conspicuous sheath ; but this continuation is 
only formed at a comparatively late stage. In Angiopteris it is present from a very 
early period, and is closely connected with the formation of the “stipules.” By 
means of Todea an explanation is afforded of the probable nature of the stipule in 
Angiopteris. As I have above pointed out, it may with good reason be regarded as an 
advanced modification of that winged conformation, so clearly seen at the base of the leaf 
in other Ferns. A similar explanation will serve also for Ceratozamia and StangeriaA 
In other forms, especially among the Cycadacece, the base of the phyllopodium shows 
* The extension of the stipnlar development transversely across the face of the phyllopoditun is not 
an isolated morphological fact: a similar extension is also to be found in the development of orbicular 
leaves, such as Hydrocotyh, Tropceolum, &c. This has been clearly shown by Goebel (‘ Yergl. Entw.,’ p. 234). 
It will remain for future observations to show how far a similar comparative treatment may be applied 
to the stipules of Dicotyledons. 
