G04 
MR. F. 0. BOWER OX THE COMPARATIVE MORPHOLOGY OF THE 
structure is in accordance with this. At the base of the leaf peculiar modifications 
are more prominent than in the Osmundacece, while in the upper part of the 
phyllopodium traces of a winged development can only be made out with difficulty. 
Its branching is exclusively monopodial, and its growth in length is, in some cases at 
least, strictly limited, the phyllopodium terminating in a blunt, rounded cone. 
Finally, in the Cycadcicece the apex of the phyllopodium is covered by a clearly 
marked layer of dermatogen ; its growth is never very conspicuously apical, though in 
Cycas, and perhaps in Dioon, it is more so than in other genera ; after the first stages 
are past, the growth is exclusively intercalary. It is from the first a bulky, rounded 
structure, but it bears in most cases well-marked and comparatively bulky lateral 
wings, extending from base to apex, and widened in the lower portions to form a 
sheath. The branching is in all cases monopodial, but the order of development of 
the branches is often basipetal. 
Drawing together these facts, it is clear that in the above series of plants there may 
be traced a progressive differentiation of the phyllopodium as a supporting organ on 
the one hand, and of the other members of higher order which develop as flattened 
expansions on the other. In the Hymenopliyllacece the difference appears to lie 
merely in the stronger development of a certain branch of each dichotomous system, 
while other branches, similar to them in origin and conformation, are of more limited 
growth, and assume a lateral position : gradually a monopodial mode of branching 
becomes prevalent (most Leptosporangiate Ferns) ; this shows a difference from the 
very first between the podium and the members of higher order which it bears, but 
the difference is again lost where there is a return to the dichotomous mode of 
branching. The next step is that the apex of the phyllopodium loses the structure 
characteristic of flattened organs, and assumes that characteristic of cylindrical 
structures (Osmundacece) , and this is maintained during the development of the lower 
portions, though in its upper parts the phyllopodium is reduced to a flattened 
structure not unlike, in form and structure, that in other Leptosporangiate Ferns. 
In the Marattiacece the apical growth is arrested, at all events in certain cases, at a 
comparatively early stage: the phyllopodium has the apical characteristics of a 
cylindrical organ, and where its growth is limited it does not resume the characters of 
a flattened organ ; it is essentially an organ adapted rather to bear the flattened 
assimilating organs, than such an organ itself, while by its exclusively monopodial 
branching it is always clearly distinguished from the branches (pinnse) which it bears. 
Finally, in the Cycctdacece the distinctive characters of the phyllopodium are still 
more accentuated ; it is from the first a bulky structure ; its apical growth is soon 
arrested ; it does not (except in a few cases, e.g., some leaves of Stangeria) develop 
as a flattened assimilating organ, but differs both genetically and in its further 
development from the pinnse which it bears. It is essentially an organ adapted to 
bear the members of higher order, on which the assimilating function mainly devolves. 
It is unfortunate for the study of the comparative morphology of the shoot that no 
