6o6 



FILICALES 



which, however, soon develops a pith. The anatomy of this Fern, which 

 deserves a thorough reinvestigation, appears to be comparable with that 

 of a solenostelic Dennstaedtia : it suggests the structure from which the 

 more complicated Cyatheaceous stems may have arisen. Another species 

 with exceptionally simple structure is stated to be A. blechnoides, which is 

 peculiar in having a trailing axis. 1 



In the vast majority of the Cyatheae the vascular system consists 

 essentially of a dictyostele, with accessory strands in the pith, and in 

 some cases in the cortex also. The leaves being closely disposed on the 



massive axis, the leaf-gaps, which 

 are narrow, overlap, and accord- 

 ingly several are traversed in a 

 single transverse section (Fig. 

 337 B). The dictyostele is thus 

 represented by several broadly 

 strap-shaped tracts, with their 

 margins turned outwards, and 

 guarded on either side by bands 

 of brown slerenchyma : this is 

 the correlative of the solenostck- 

 of simpler types. The leaf- 

 trace, composed from the first 

 of numerous distinct strands, 

 springs from the margin of the 

 leaf-gap, the strands being dis- 

 posed in the usual horse-shoe 

 series. But over and above 

 this fundamental vascular system 

 accessory strands are found in 

 the pith (Figs. 337 A, B) : these 

 originate from the foliar gaps, 

 and traverse the pith as a 

 branched system with occasional 

 blind endings. In origin and nature they would appear to be comparable 

 to the accessory rods seen within the solenostele in Dennstaedtia rubiginosa 

 (compare Fig. 333)- 2 In the cortex also an accessory series of strands, 

 related to the leaf-trace, is found : it is well shown in C. Imrayana 

 in Fig. 337 c, and is reported also for other species, both of Cyatlica 

 and of AlsopJiila. This cortical system has no recognised correlative in 

 other Ferns. 



Young plants of Alsophila excelsa have been examined by Gwynne- 

 Yaughan, 3 with a view to tracing the ontogeny of the vascular system, and 

 especially the origin of the medullary strands : his results are illustrated 



1 Mcttenius, Ucber .-///;/<</>/< 7 vV, p. 524, note 3. 



2 Gwynne-Vaughan, /.c., p. 709. :i /..<.. p. 709. 



Cyathca linrfiyaiia, Hook. Transverse section of stem. 

 Natural size. At b, c, d, foliar gaps ; all the black bands and 

 spots are stereom, all the paler bands are vascular strands 

 in section. The letters a, s, /,_/have the same meaning as 

 in Fig. 337 A. (After De Bary.) 



