316 Dr. G. Ogilvie on the Vascular 



stance, which is deficient in the rhizome, makes its appearance in 

 the petioles as sheaths of dark tissue round the vascular fasci- 

 culi. In Asplenium lanceolatum, in which there is no dark sheath 

 of this kind, the scalariform vessels and cambium-layer of the 

 fasciculi become themselves the seat of a deposit of dark sub- 

 stance, by which they are not merely tinged brown as in L. Filix 

 mas, but the cavities of the vessels are more or less filled up. 

 The induration is confined, so far as I have observed, to the 

 fasciculi near the base of the petiole, not extending either up- 

 wards towards the frond, or downwards into the rhizome. 



In all the species, indeed, now mentioned, the dark tracts 

 stop short just above the origin of the petioles from the root- 

 stock ; but there are others in which they pass some way into 

 the substance of the latter, accompanying the vascular bundles 

 to their junction with the netted cylinder, and even bordering 

 some of the anastomosing fasciculi by whose interlacement the 

 cylinder is formed, so that they appear as dark spots in a trans- 

 verse section of the rhizome. 



Thus in Scolopendrium vulgare, in which we find in each 

 petiole two vascular fasciculi, running into one above in the 

 midrib of the frond, these are accompanied, from their origin 

 in the rhizome, by dark lines on their outer margins. In the 

 petiole itself, a little above the base, other dark lines appear on 

 the inner margins of the fasciculi, gradually expanding, as they 

 ascend, into two half-sheaths, which become united by their 

 convexities as the fasciculi approach, and finally stop short at 

 the point of junction of the latter, while the outer marginal 

 lines run far on, along the midrib of the frond. The general 

 arrangement of these parts is illustrated in Plate VI. figs. 1, 2, 3. 



In Ceterach officinarum (Scolopendrium Ceterach, Grammitis 

 Ceterach) the two fasciculi of the petiole are accompanied, from 

 their origin in the netted cylinder, by three dark lines — two on 

 the outer margins, and one median, the latter at first somewhat 

 on the upper or inner aspect of the petiole, but gradually in- 

 sinuating itself between the fasciculi, so as to form two half- 

 sheaths united by their convexities, as in the last species. Higher 

 up in the petiole, where the fasciculi unite into a single vascular 

 cord in the midrib of the frond, the median tract of dark tissue 

 comes to lie on its upper surface, the others continuing to run 

 along its lateral margins. 



In Lastrea Oreopteris the petiole has two fasciculi of scalariform 

 vessels, and on the inner margin of each (that lying next to the 

 axis of the stalk) a chain of dark-coloured cells — sometimes 

 continuous, sometimes interrupted. The two chains unite be- 

 low, like the sides of the letter V, just above the junction of the 

 vascular bundles of the petiole with those of the netted cylinder 



