VASCULAR FASCICULI IN BRITISH FERNS. 85 
external characteristics with W. Oreopteris, but also greatly re- 
sembles that species in the form and arrangement of the vascular 
bundles of its stipes. For instance, in a fertile frond, 26 inches 
long, which I examined, where the stipes measured 12 inches, 
though the vascular tract could be clearly traced sending a branch 
of a greenish tint into each pinna, yet there was no sign of the 
prolongation of the dark sheath so conspicuous in each vascular 
bundle of the stipes in this fern, and which is an almost invariable 
element in the other British ephrodia (Lastree). Now the 
dark sheath is not partially only, but entirely wanting in JN. Oreo- 
pteris. Figs. 4 a, 4 b, 4 c, and 4 d represent transverse stipital 
sections made respectively at the junction of stem and stipes, and 
at 3, 6, and 9 inches above that point; figs. 4 e and 4 f, similar 
sections at further intervals of 14 inch. It will be seen that 
the two large oval vascular bundles have coalesced at 10j inches 
from the origin of the stipes, and 13 inch below the first pair of 
pinne. At and near the origin of the stipes its cortical layer is 
thick, dense, and dark, as shown in 4a. Above, as the dark sheaths 
of the fibro-vascular bundles are more marked, and their constituent 
cells more lignified by secondary deposits, so the cortical layer 
becomes paler and thinner: this observation has been made fre- 
quently with reference to other species of ferns. In figs. 1, 2, 
& 3, a remarkable difference in the arrangement of the scalari- 
form ducts in the midst of the smaller cells of the fibro-vascular 
bundles is noticeable. These spiral-fibrous or, rather, scalariform 
ducts are arranged for the most part, both in Nephrodiwm Thely- 
pteris and in the closely allied species JV. Oreopteris, in the form of 
the Greek letter X,—the more usual form being that shown in 
fig. 1, which is, with slight variations, common to all the other 
British Nephrodia and Aspidia*. Here, all the larger cells of the 
two main fasciculi¢ near the axis of the stem are grouped together 
* In the genus Lastrea, L. recurva (Fenisecii), with its very compound 
fronds of almost deltoid outline, its dark ramenta, and the trilobed outline dis- 
played by a transverse section of its stipes, passes, by nearly insensible grada- 
tions, through Zastrea dilatata and its slightly divergent varieties, —through 
Mr. Westcombe’s new form L. Scotica,—through the forms L. glandulosa, L. 
spinulosa, and L. uliginosa, to L. eristata with its simpler narrow fronds, its 
pale concolorous ramenta, and its quadrangular section, —the disposition of the 
Vascular fasciculi remaining nevertheless nearly identical in the whole series. 
T In the British Lastreas, &c. (excepting, of course, L. Oreopteris and L. 
Thelypteris), the number of the fasciculi, though never less than three, is by no 
means a constant character, sometimes as many as eleyen or thirteen being found 
in a large and vigorous frond. Frequent branching and anastomosing of the 
