MARATTIACEAE 525 
It will be unnecessary to describe it in detail here: our object will be 
rather to bring it into relation with the less complex systems of other 
Ferns, and with the cognate fossils. This is most readily done by reference 
to the seedling-structure, and to those genera which are less complicated 
in their mature state; for there is considerable variety of complexity in 
the different living genera of the family. It is found that Aawzdfwssia and 
Archangtopterts are relatively simple, while Axgiopter’s is the most 
complicated of all, J/arattia and Danaea 
taking a middle position. 
In the seedlings of them all the axis 
is traversed by a monostele: in Danaea 
simplicifolia it has a solid xylem-core, 
which is maintained till several leaf-traces 
have been given off from it, naturally 
without any leaf-gap:1 it then becomes 
crescentic, and expands into a dictyostele 
with leaf-gaps, while a central strand or 
commissure arises from the concavity of the 
dictyostele, and pursues an upward course 
with occasional fusions at the successive 
leaf-gaps.° The same type of structure is 
closely followed in the mature stem of 
Archangiopterts,® though on a simpler scale ; 
in fact, this stem still retains at maturity a 
stage rapidly passed through by the young 
plants of other more complex genera. A 
similar vascular system, consisting of a 
cylindrical dictyostele, with normally a 
Fic. 291. 
; ‘ 3 Angiopteris evecta. Stele of a young 
single central strand, 1s found also in the plant showing. the foliakeape. 2s Date 
mature axis of Kaw/fusséa; but it is dorsi- Hill) vi=root-trace..(After, Rarmenand 
ventral, and rather more elongated between 
the leaf-gaps, in accordance with its creeping habit! In mgzopfer’s and 
Marattia the final structure is more complex, though the initial steps are 
similar. There is in their seedlings also a solid protostele: in the central 
part of its xylem-core certain cell-rows cease to differentiate as tracheides, 
but give rise to a parenchymatous pith: the siphonostele thus formed 
becomes broken up by leaf-gaps, thus giving rise to a dictyostelic cylinder ® 
(Fig. 291). Subsequently, as the stem passes to maturity, there arise 
'But Jeffrey (Pr2l. Trans., 1892, B, vol. excv., p. 120, etc.) states that in several 
species of Danaea the stele is tubular in the seedling, and that it is interrupted by leaf-gaps. 
That may be so in older conditions, and Jeffrey’s material does not appear to have 
been young enough to decide the question for the earliest stages. 
2;Brebner, Anz. of Bot., Xvi., p. 524. 
3>Gwynne-Vaughan, Azz. of Bot., xix., p. 259. *Kiihn, Alora, 1889, p. 475. 
>’ Farmer and Hill, Azz. of Bot., xvi., p. 371. 
