LEAF IN THE VASCULAR CRYPTOGAMS AND GYMNOSPERMS. 
G03 
branching of the phyllopodium, it is in many cases undoubtedly monopodial, though 
in the higher ramifications there is frequently a return to the dichotomous mode of 
branching. As is well known, the apical growth in some cases may be unlimited 
(Lygodium ). Thus in the majority of the Leptosporangiate Ferns the phyllopodium 
is more clearly differentiated from the members which it bears than is the case in the 
Hymenophyllacece, and this is most clearly marked by the prevalence of a monopodial 
branching at least in the earlier ramifications. But the structure of the apex is still 
that characteristic of flattened organs, and when dichotomy occurs in its higher 
ramifications, it is no more distinct from the members of higher order which it bears 
than is the case in the Hymenophyllacece. 
In the phyllopodium of the Osmundacece the two-sided apical cell as found in other 
Leptosporangiate Ferns is replaced by a three-sided, conical, apiccd cell, and it is 
believed that these are the only plants in which a three-sided cell has been found at 
the apex of the leaf.' 1 ' Thus the arrangement of the apical meristem is that charac¬ 
teristic not of flattened, but of cylindrical organs, and this may be regarded as indi¬ 
cating an advance in robustness of character, and therefore in adaptation to serve as 
a supporting organ. But the change is not accompanied by any marked difference of 
external conformation of the phyllopodium as a whole : it is still a winged structure, 
though the wings cannot be traced in the lower parts of the leaf as originating from any 
definite marginal series of cells. The position of the apical cell is such as to correspond 
to the requirement of a more bulky development of the phyllopodium on the dorsal side, 
the greater part of the tissues derived from the two dorsal series of segments being 
devoted to the building up of the bulky dorsal part of the phyllopodium, while the 
wings and pinnae are derived partly from the edges of the dorsal segments, partly 
from the ventral segments. It is clear that a three-sided apical cell is better adapted 
to a leaf with a bulky winged phyllopodium than a two-sided one, and in this sense 
the structure of the apex of the phyllopodium in the Osmundacece may be regarded as 
an advance upon that in other Leptosporangiate Ferns. The branching of the phyllo¬ 
podium in the Osmundacece is monopodial, and no example of dichotomy has been 
observed in the higher ramifications, at least in Osmunda regalis : thus the phyllo¬ 
podium preserves its identity throughout the leaf, as distinct from the pinnse which 
it bears ; and this is not the case in those Leptosporangiate Ferns in which it branches 
dichotomously. At the base of the phyllopodium there are peculiar modifications of 
the winged structure, which will be discussed again later. 
In Angiopteris, as an example of the Marattiacece, there is no single apical cell 
occupying the bulky apex of the phyllopodium, but a group (four) of apical cells give 
rise, by their repeated divisions, to the tissues of the leaf, which thus approaches in 
the arrangement of its apical meristem to that characteristic of the higher plants. 
The apex of the phyllopudiuin is not flattened, but cylindrical-conical, and its internal 
* Hoi.le asserts that there is a wedge-shaped cell at the apex of the leaf of Angiopteris, and describes it 
as being of “ irregular cross-section ” : on this point compare my own observations as above detailed. 
4 H 2 
