318 Dr. G. Ogilvie on the Vascular 



bundles corresponding to the netted cylinder of other Ferns, 

 though, from the way in which the stem is drawn out longitu- 

 dinally, the reticulations are represented only by long wide slits 

 formed by the irregular anastomosis of the bundles. Inside the 

 more external layer of parenchyma containing these bundles are 

 two dark bands, of a hard woody nature, running the whole 

 length of the rhizome, — one on its upper, and the other on its 

 under aspect. The former is flat; the latter, which is broader, 

 is turned at the edges, like the sides of a boat ; so that the two 

 together partially enclose the axis or central portion of the stem, 

 consisting of soft white parenchyma, like that on their exterior. 

 But the great peculiarity of the rhizome of P. aquilina, in which 

 it differs from all our other Ferns, is the occurrence of a second 

 vascular system in this central region, consisting of two bands 

 or broad fasciculi lying immediately on the inner aspect of the 

 woody tracts (PL VI. fig. 7). The fasciculi are in the main di- 

 stinct from each other, and from those of the outer series, though 

 there is an occasional communication by anastomosing fibres. 

 In the same way the two woody bands are generally quite di- 

 stinct, though here and there they may become fused together 

 for a space, on one or both sides, so as in the latter case to form 

 a complete ring round the medullary parenchyma and the vas- 

 cular fasciculi imbedded in it. This occurs at points where 

 several fronds are given off in close proximity — a circum- 

 stance which affects the disposition of the tissues of the stem, 

 both woody and vascular, in consequence of these branching out 

 to form the corresponding tissues of the petioles. In the petiole 

 the main tract of dark tissue forms a plaited band, having a 

 T-shaped section, — the perpendicular lamina, which lies towards 

 the inner aspect of the petiole, arising mainly from the upper 

 band of the rhizome, and the fluted transverse lamina from the 

 lower. These central plates, along with subsidiary and more 

 superficial tracts, arising in the petiole itself, serve partially to 

 ensheath the numerous fasciculi of vessels which are derived 

 from both the vascular systems of the rhizome, outer and inner 

 (PL VI. fig. 8). The brown tint and woody character of the 

 plates disappear in the upper part of the petiole, their tissue 

 merging into the general parenchyma of the part. The paren- 

 chyma of the rhizome, both medullary and cortical, is also 

 marked occasionally with interrupted striae of brown tissue, 

 like those occurring in the medullary parenchyma of Lastrea 

 dilatata, but much more attenuated, and of very considerable 

 length. 



In Allosorus crispus(Cryptogramma crispa) there is a perceptible 

 tracery of dark tissue round the several fasciculi of the netted 

 cylinder; but the principal accumulation is along the axis of the 



