and Woody Tissues of Ferns, 317 



of the rhizome. A horizontal section of the rhizome shows these 

 tracts in section as dark spots on the contiguous margins of such 

 of the vascular bundles as have been divided a little above the 

 point of convergence (PL V. fig. 6) . 



In Asplenium Ruta muraria, instead of these dark lines, we 

 have, near the base of the petiole, a complete sheath of brown 

 tissue surrounding the single central vascular fasciculus (PI. V. 

 fig. 8). In the rhizome, the sheaths of the petiolar fasciculi be- 

 come reduced to dark lines on the outer and inner margins of 

 the vascular bundles which go to join the netted cylinder ; and 

 on a horizontal section, they are represented by a series of black 

 spots on each side of the interrupted circle formed by the cut 

 extremities of these bundles, but most distinctly on the inside. 

 In Asplenium Trichomanes the arrangement is somewhat similar, 

 but the dark sheaths round the petiolar fasciculi appear to be 

 mainly derived from the brown cortex or tegumentary invest- 

 ment of the bases of the petioles. 



But the darker spots seen in a horizontal section of the rhi- 

 zome are not always due to the prolongation downwards of the 

 lines of brown tissue belonging to the petioles. In Lastrea dila- 

 tata there occur in the medullary parenchyma (that is, inside 

 the circle formed by the netted vascular cylinder) numerous 

 isolated fusiform nodules, with their long diameter parallel to 

 the axis of the rhizome. Each nodule consists of a few short 

 cells placed end to end and filled with a very dark, almost black 

 deposit (PI. V. fig. 7)*. This species has its petiolar fasciculi 

 ensheathed with dark tissue, as in its congener L. Filix mas ; but 

 these sheaths disappear near the base of the petiole, and there 

 is no connexion between them and the nodules in the centre of 

 the rhizome. 



The nodules in L. dilatata may be considered as an example 

 of the first degree of induration in the rhizome ; in the species 

 which remain to be noticed the amount of dark tissue is much 

 more considerable. In Pteris aquilina and Allosorus crispus 

 there are continuous bands or cords running the whole length 

 of the stems ; and in Blechnum boreale, Osmunda regalis, and 

 Hymenophyllum, the dark tissue really makes up the principal 

 mass of the rhizome. 



In Pteris aquilina the creeping rhizome is invested by a villose 

 integument of a hard leathery consistence, formed of rounded 

 cells indurated by the dark deposit. In the pulpy and lubricous 

 parenchyma immediately underneath, there is a series of vascular 



* The allied species or variety L. Foenisecii, which, I am informed by 

 Prof. Balfour of Edinburgh, is remarkable for the dark colour of the cen- 

 tral part of the rhizome, probably owes this peculiarity to the great deve- 

 lopment of these dark nodules. 



