514 INTKODUGTION TO CEYPTOGAMIC BOTANY. 



of the same importance as in Endogens and Exogens. To 

 take the cases of deciduous-leaved tree ferns and Murcdtiacew, 

 nothing can be more different in the whole group than the 

 disposition of their tissues. That the rhizoma will in some 

 cases afford good characters, as also the disposition of the vas- 

 cular bundles in the stipes, can scarcely admit of doubt. 



575. The Rhizoma, as just said, varies greatly in character. 

 In some cases, as in Marattia, the vascular bundles are 

 regularly distributed through the whole mass ; in others they 

 are disposed in a single circle, as in Nephrodiuin Filix Mas, 

 or with neighbouring smaller bundles, as in Phymatodes 

 leiorhiza ; m others they are reduced, as in Trichomanes 

 reniforme, to one central bundle ; while in others they are 

 disposed on either side of hard plates, as in Pteris aquilina ; 

 or a few larger than the rest, as in many tree ferns, are 

 closely surrounded with dense tissue, and disposed symmetri- 

 cally round the axis, sometimes forming a closed cylinder, as 

 in Picksonia antarctioa* In some cases they seem to be quite 

 insolated, giving off no bundles to the fronds, this office being 

 performed by smaller fascicles, as in the tree ferns figured by 

 Mohl in Martius's work on the Cryptogams of Brazil ; while 

 in others they as evidently supply the stipites. 



576. The general disposition of the tissues in the more 

 highly organized ferns may be given as follows : — Round the 

 scars of the stipites cavities exist filled with stellate brown 

 tissue. The cortical stratum consists first of cuticle, then of 

 parenchym, and then of hard brown parenchym,-f- with thick 

 punctated walls. The inclosed cylinder is filled with softer cel- 

 lular tissue, containing many cysts gorged with resinous matter, 

 and various bundles of vascular tissue, attended by pale pleu- 

 renchym. The larger bundles, which are flattened and variously 

 curved, are surrounded by dense tissue like the inner layer of 



wliich the stipe is not articulated, as Nc ijlir odium Filix Mas, Desmohrya. 

 Contiguous genera, as NepJirolepis and NepliTodium, Stenochlcena, and 

 Polyhotrya, sometimes belong to the two divisions. 



* I have a portion of a tree fern from Silhet, given me by Dr. Hooker, 

 in which the cylinder is nearly perfect. See also Lind. Veg. King. 



t This tissue is sometimes parenchym, sometimes prosenohym. 



