52 PTEROID FERNS [cn. 



show other features of advance than in the sorus only. In the vegetative 

 system there is a constant presence of protective scales in place of hairs 

 alone, an advancing disintegration of the vascular tracts, and a frequent 

 integration of leaf-surfaces, with which goes also an advancing reticulation 

 of the veins. These remarks are made in advance of the statement of the 

 facts upon which they are based, so as to clarify the exposition that is to 

 follow. 



Flattened scales are universally present on the rhizome and leaf-bases of 

 species of Pteris: they may be accompanied by simple hairs. This is in broad 

 contrast to the Dicksonia-Dennstaedtia series from which these Ferns were 

 presumably derived. The simple hairs there seen are repeated in the bi- 

 indusiate Pteroids, such as Pteridhim and Paesia; but for some reason which 

 is obscure the protective scale appears in the genera Lonchitis and Histi- 

 opteris, while coincidently the inner indusium is obliterated. The remarkable 

 point is not that there should be a divergence in this respect, as we have 

 seen, between the two species of Lonchitis, but that there should be any near 

 relation between the incidence of features so distinct as dermal scales and a 

 lower indusium. Such facts tend to establish both as trustworthy data for 

 broad comparison in a progression which involves so many variable features. 

 They accentuate the recognition of the recurrent protective scales in Pteris 

 as a feature of advance in a genus where the lower indusium is always 

 wanting. 



In so large a genus as Pteris^ including ferns sometimes with long creeping 

 rhizomes, as in P. grandifolia, sometimes with a compact upright habit, as 

 in P. longifolia, cretica, ox podophylla, some variation in vascular structure is 

 to be expected. A general comparison relates them all as natural derivatives 

 from solenostely with an undivided leaf-trace, such as is characteristic of 

 their probable Dennstaedtioid source. The species investigated range between 

 typically solenostelic structure and a complicated polycyclic dict}'ostely: 

 while the leaf-trace varies from an uninterrupted horse-shoe to two straps 

 originating separately from the stele of the axis. Typical solenostely is seen 

 in P . grandifolia, where there is a long creeping rhizome. A transition to 

 dictyostely with overlapping leaf-gaps appears in many more compact or 

 ascending shoots, such as P. treinula, cretica, JIabel/ata, JieteropJiylla, pellucida, 

 biaurita, and Szvartziana. In most of these the leaf-trace remains undivided; 

 but in some, such as P. cretica, it appears as two separate straps, though 

 these may fuse upwards. 



A more marked modification is seen in the presence of accessory vascular 

 strands. A relatively simple case has been described at length by Gwynne- 

 Vaughan in P. {Litobrochia) Kunzeana Ag. {P. data van Karsteniana Kze.). 

 Here the erect or oblique rhizome contains a perfect solenostele with an 

 internal vascular cylinder connected at each node with the outer by a com- 



