526 FILICALES 



within the cylinder of Angiopteris three or four crescentic-meshed zones 

 of vascular tissue, and it has been stated that there is here again a 

 single central strand. 1 Marattia resembles Angiopteris, 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 Psaronius : 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 Angiopteris, the former 

 being disintegrated in the modern Ferns, in conformity with the disintegrated 

 leaf-traces with which they are connected. 2 



1 Mettenius, Abhandl. Konigl. Sachs. Ges. d. Wiss., vi. ; Miss Shove, Ann. of Bot., 

 xiv., p. 497. 



2 It 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 Euphioglossum^ which is held to be the more primitive section of the 

 genus, the leaf-trace is a single broad strand : in Ophioderma, 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. 



