526 FILICALES 
within the cylinder of Amgzopteris three or four crescentic-meshed zones 
of vascular tissue, and it has been stated that there is here again a 
single central.strand.1 Marattza resembles Angiopterts, but does not obtain 
so high complexity. 
As regards the attachment of the appendages, the vascular supply to the 
mature leaves originates as many distinct strands from the dictyostele: this 
is obvious enough in the simpler cases, but it appears to hold also for the 
more complex: here the leaf-trace is stated to spring from the outermost 
zone only. The roots, on the other hand, originate even in the simpler 
forms, in close relation to the central strand, while in the more complex 
they mostly spring from various points in the internal system, but some 
also from the outer zone. . 
It is thus seen that the ontogeny opens in all cases with a monostelic 
state, with a solid xylem-core. This gives a basis for comparison with 
other types of Fern, where the monostele is permanent. It is in the ' 
later phases of the individual life that the complications arise, and it will 
be recognised that these vary in rough proportion to the size and complexity 
of the whole shoot, and are most complex in the large plants of 
Angiopteris. 
Comparing the structure of the fossil Marattiaceous stems with that 
of the, living genera there are marked differences, though the points of 
similarity suffice to indicate a true relationship. The casts show on their 
smooth leaf-scars that the leaf-trace was habitually a continuous vascular 
band (Fig. 280), while that of all the modern Marattiaceae is composed of 
numerous independent strands: the latter are, however, disposed in series, 
of which the outermost corresponds in outline to one of those continuous 
bands, as though it had been broken up. This greater coherence of 
the vascular tracts is characteristic also of the stem of Psavonzus: for the 
centre of these fossils is occupied by numerous broad band-like plates, 
disposed in concentric series, which show differences in relation to the 
phyllotaxis. These series of vascular plates are doubtless the correlatives 
of the meshed zones seen in the mature stems of Angiopéeris, the former 
being disintegrated in the modern Ferns, in conformity with the disintegrated 
leaf-traces with which they are connected.? 
1Mettenius, Abhandl. Kénigl. Sachs. Ges. d. Wiss., vi; Miss Shove, Ann. of Bot., 
xiv., Pp. 497. 
2It is interesting to compare this disintegration of vascular strands seen in the modern 
Marattiaceae while the related fossils show connected vascular bands, with the analogous 
cases seen in other Ferns. It will be shown below that most of the Simplices have a 
single vascular band of the leaf-trace, while the larger Gradatae have a leaf-trace composed 
of many smaller strands. A parallel is also seen in the Ophioglossaceae: it has been 
shown that in Zuphzoglossum, which is held to be the more primitive section of the 
‘genus, the leaf-trace is a single broad strand: in Ophzoderma, which is held to comprise 
derivative forms, the leaf-trace consists of several distinct strands, It seems probable 
that a progressive disintegration of a primitively simple leaf-trace has been a wide-spread 
phenomenon in the evolution of large-leaved types. 
