and Woody Tissues of Ferns. 321 



terposed between them and the dark cortical portion of the stem, 

 it is hardly possible to separate the vascular coat in the same 

 way from the delicate cellular tissue of the medulla which it in- 

 vests. (PL V. fig. 3 ; compare with fig. 4.) 



The rhizomes of Hymenophyllum Tunbridgense and H. Wil- 

 soni are of interest from presenting a transition to the type of 

 stem characteristic of the Lycopodiacese, as there is but a single 

 vascular bundle, lying in the axis of the bristle-like rhizome 

 (PL VI. fig. 5). This central fasciculus contains four or five 

 scalariform vessels, surrounded by a cambium-layer. Round 

 this, again, there is a thin stratum of pale parenchyma, and a 

 cortical layer of brown tissue, fibrous and much indurated inter- 

 nally, but loose and chaffy on the exterior. The transition-cha- 

 racter of the stem is of the more interest that we have in it 

 all the essentials of the rhizome of Osmunda. We have only to 

 conceive the stout caudex of the latter drawn out till it is reduced 

 to the thread-like dimensions of the rhizome of Hymenophyllum, 

 to have a complete transformation of the one into the other ; 

 for when the vascular cord of Osmunda is reduced to the dimen- 

 sions of that of Hymenophyllum, its cellular pith necessarily 

 disappears, as a single series of vessels of the ordinary thickness 

 must come to occupy its whole diameter. 



In all the stems noticed above, with the dark tissue much 

 developed, and particularly in Osmunda regalis, Blechnum boreale, 

 Pteris aquilina, and Allosorus crispus, there is a very remarkable 

 contrast between the hardness of the coloured tracts and the 

 great softness and delicacy of the pale parenchyma and of the 

 vascular bundles (especially in their cambium-layer). The close 

 juxtaposition of tissues of such different powers of resistance 

 adds much to the difficulty of obtaining thin sections for micro- 

 scopical purposes. The permanency of these tissues is in pro- 

 portion to their hardness. Thus in the rhizomes of the com- 

 mon Braken, after long exposure the cortical layer and the two 

 internal bands of dark substance are sometimes the only parts 

 left, the pale parenchyma and the vascular bundles having all 

 disappeared by the process of natural decay. And when this 

 dark substance forms the main element, as in Osmunda and 

 Blechnum, the whole rootstock has a like protracted duration, as 

 has been already observed of the former species. 



In connexion with this subject, the question suggests itself, 

 whether the hard brown tissue now referred to (or phceenchyma, as 

 it might be called) corresponds to the proper wood of the higher 

 or phanerogamic plants ? There is some difficulty in answering 

 this question, arising principally out of the ambiguity of the 

 term " woody tissue." I do not see any reason to doubt that in 

 many of the higher plants there are hard parts, commonly called 



