and Woody Tissues of Ferns. 315 



parenchyma become the seat of such a deposit, so that a section 

 commonly shows the pale tissue of the stem relieved by a dark 

 pattern of the indurated cells, as well as by the cut ends of the 

 vascular bundles, which are generally of a whiter colour. This 

 induration of the parenchymatous cells is sometimes not attended 

 by any alteration in their form, the resulting tissue somewhat 

 resembling that of the shells of nuts. In certain cases, however, 

 the cells become elongated into fibres ; and we find every variety 

 of brown tissue, from one of short cells like those of the husky 

 structures of the higher plants, to long fusiform fibres, undi- 

 stinguishable, except in colour, from the wood of the Phanero- 

 gamia. The wood- like tissue generally occurs in cords or bands, 

 either surrounding the vascular bundles or interposed between 

 two sets of fasciculi. In the denser fibrous bands the cells be- 

 come so filled up with brown matter that only a small central 

 cavity is left, as in the duramen fibres of the harder woods ; but 

 in the less indurated tracts the cells (both prosenchymatous and 

 parenchymatous) have frequently a large central space filled 

 with starch- grains, like those of the pale-coloured cellular matrix 

 of the stem. Starch-grains, it may be observed, occur in a 

 similar way in the woody fibres of the ivy, and probably in those 

 of Banksia and a few other plants, though this arrangement is 

 not usual among Phanerogamia. 



The disposition of the tracts of indurated tissue differs very 

 much, as I have already remarked, in different species. There 

 are some instances in which the brown deposit appears to be 

 confined to the layers of cells forming the cuticular investment 

 of the rhizome and of the bases of the petioles near their origin 

 from the rhizome. This is the case, more or less distinctly, in 

 all our Polypodies, in the majority of the species of Asplenium, 

 and in Polystichum aculeatum, Lastrea Filix mas, and Adiantum 

 Capillus Veneris. 



The deficiency is most marked in the nodulated stems of the 

 common Polypody ; their peculiar fragility is due to the soft 

 watery parenchyma in which the minute and straggling vascular 

 bundles are imbedded. In most of the other species there is, 

 more or less, some compensating provision. Thus in Polypodium 

 Dryopteris, and still more in P. Phegopteris, the parenchyma is 

 much denser, and has a decidedly dark or brownish tinge. In 

 Asplenium Filix fozmina, there is no such dark tinge in the fresh 

 parenchyma, but it has a peculiar hardness, from the thickness 

 of the walls of its component cells. In Lastrea Filix mas, again, 

 the vascular bundles have a brownish tint, and a degree of tena- 

 city which allows them to be dissected out with more ease than 

 in any other of our Ferns. 



We find, too, that in many of these species the brown sub- 



21* 



