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Phylloglossum Drummondii . 
in the former being paralleled in the latter by the strong development of 
secondary cortex. We are reminded, in this connexion, of the notably 
strong development of secondary cortex in many fossil forms. 
The leaves, again, of the two forms are noticeably alike in shape, at 
least in the upper and greater part of their length ; while in both, the leaves 
are large relatively to the stem, in spite of their ‘ microphyllous ’ anatomy. 
The presence of phloem in the stem is much more problematical in 
Phylloglossum than in Isoetes ; indeed it may be said to be entirely absent. 
True phloem probably exists, as we have seen, in the leaves of the former, 
the single leaf-bundle being concentric. 
The mesarchy seen in the lower part of the leaf of Isoetes is reflected 
in Phylloglossum , in which plant, however, this condition is much more 
general, as it occurs throughout the leaf, in the upper part of the stem, in 
the peduncle and axis of the strobilus, and even in the strand of the 
young tuber. 
In both Isoetes and Phylloglossum the vascular system is cauline, and 
the leaf-trace bundles leave the stele—a protostele in both cases—un¬ 
disturbed by their exit. 
The protoxylem cavities, so prevalent in Phylloglossum , occur con¬ 
stantly in the leaf of Isoetes. 
The roots in both are monarch in structure. 
In fact the external and internal morphology of the vegetative Organs 
in the two plants are remarkably alike in fundamental points, suggesting 
additional evidence of the Lycopodinean affinities of Isoetes. 
There seem at first sight, on the other hand, to be important differences 
in the structure of the reproductive organs. This feature, however, is 
mainly due to the adoption of the heterosporous habit of Isoetes. With 
this are probably connected the ligule and the * velum ’—structures which 
have been paralleled with those found in the integumented sporangia of 
Miadesmia ; many may consider, in fact, that Isoetes has advanced beyond 
mere heterospory ; it has made the first step towards seed-production. We 
may suggest that the homosporous Phylloglossum could not proceed so 
far, at least in this direction ; but in specialization for spore dispersal it is 
a decided advance upon Isoetes , as its sporangia are aggregated into a very 
definite and pedicellate cone. It shares, of course, with Isoetes the constant 
Lycopod character of one sporangium to each sporophyll. 
The structure and development of the individual sporangia have been 
exhaustively described by previous authors; it will suffice to recall here 
the fact that the sporangium is typically Lycopodinean, and of the less 
specialized, Urostachya , type. 1 
4. Let us now proceed to consider the question of the primitiveness, 
or otherwise, of Phylloglossum. 
1 Sykes ( 11 ). 
