300 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [ Mar. 9, 
or slits passed upwards and outwards through the cylinder; and in 
transyerse section they are seen either completely breaking up by a 
thin film of cellular tissue the continuity of the cylinder, or only 
penetrating it for a short distance. Such partial penetrations 
sometimes proceed from the inside and sometimes from the out- 
side of the cylinder, depending upon the part of the particular 
mesh which has been cut. When the mesh is cut near its origin, 
the cylinder is complete on its outer margin; while when it is 
cut through the upper portion, the cylinder is complete on its 
inner margin. Dr. Ogilvie, in a valuable paper on the vascular 
and woody tissues of ferns (Annals and Magazine of Nat. History, 
ord ser. vol. vi. (1860) p. 320, pl. v.), has somewhat misinter- 
preted this vascular cylinder in Osmunda regalis. He says the 
cylinder is made up of about eight fascicul, having the same 
crescentic section as the vascular bundle in the petiole, and having 
their concavities all turned inwards. This is figured and de- 
scribed in plate v. fig 1. His error arises from his entertaining 
the notion that the vascular cylinder is composed of the fasciculi of 
the petioles, which, when they descend into the stem, branch out and 
anastomose with those derived from former petioles. This cylinder, 
however, 1s formed independently of the food-producing leaves, or 
at all events in advance of them; and the meshes are really the 
openings through which the fasciculi pass to the leaves. These 
meshes do not in any way represent the reticulations caused by the 
medullary rays in the wood of Dicotyledons. They are homologous 
with the meshes produced by the tissues which pass through the wood 
into the foliar or ramal appendages. 
The vascular cylinder of the stem is surrounded by a thin layer 
of pale parenchyma similar to that composing the axis. Dr. Ogilvie 
calls this a cambium layer; but he overlooks the fact that the vascular 
bundles in ferns are definite and simultaneous, and that a cambium 
layer does not exist in this position. 
The vascular bundles of the petioles spring from the meshes in 
the vascular cylinder. At their origin they have the crescentic form 
which characterizes them throughout their whole course in the 
petiole and rachis, as well as all the branches in the secondary 
rachides. ach petiole is composed of its vascular bundle, having 
the concavity of the crescent looking towards the axis of the stem. 
This is imbedded in a pale parenchyma, composed of slightly oblong 
cells; and the whole is surrounded by a cortical layer of smaller but 
more elongated cells, deeply coloured by the deposit in their interior 
of the brown-coloured substance so extensively distributed in ferns, 
and which is said, from its abundance in them, to give a peculiar rusty 
tint to the vegetation of those districts in which (as in some parts of 
New Zealand) ferns form a prevailing feature. Near the base the 
petiole is furnished with a wing, which is composed of white cellular 
tissue enclosed in a thin epidermis. In addition to the colouring- 
matter in the cortical layer of the petiole, a few small bundles of 
elongated cells occur irregularly scattered through the central paren- 
chyma, both in the hollow concavity of the vascular bundle and on 
