a New Fern from the Coal-Measures. 209 
peripheral part of the phloem of each vascular bundle ; these 
small canals are quite distinct from the larger ones in the 
ground-tissue of the petiole, and do not exist in the genus 
Myeloxylon. 
Description of Specimens from Professor 
Williamson’s Collection. 
In transverse section the petiole Rachiopteris Williamsoni 
presents an irregular outline, with its longest diameter about 
2 cm. ; the characteristic Myeloxylon form of hypoderm 
is readily detected when the sections are examined with 
a pocket lens. In some of the transverse sections a band of 
parenchymatous tissue is seen external to the hypoderm, and 
the outermost layer of this tissue forms a fairly well marked 
epidermis (Fig. 1). Internal to the hypoderm is the funda- 
mental parenchyma with its numerous secretory canals and 
scattered vascular bundles, the whole arrangement being very 
similar to that in Myeloxylon. In one section (Cabinet Number 
282 *) there is seen to be a mass of parenchymatous tissue in 
close contact at one point with the outermost cells of the 
petiole. This parenchyma consists of narrow and radially 
elongated cells, and towards its outer edge presents a ragged 
appearance ; associated with it is a considerable quantity of 
some black substance, the whole being suggestive of a scaly or 
laminar outgrowth from the surface of the petiole, and in part 
consisting of secretory cells. It is, however, impossible to 
give any satisfactory account of this peculiar structure, and we 
need not further concern ourselves with its probable nature. 
Fig. 2 is from a photograph of a transverse section of the 
petiole; the hypoderm is shown as a dark band — h. and the 
lighter coloured patch of tissue, a , is the parenchymatous 
outgrowth to which reference has just been made. 
We may pass on at once to a more detailed description of 
the transverse and longitudinal sections. 
In some parts of the periphery of one of the transverse 
sections (C. N. 278), there is a fairly distinct epidermal layer 
Prof. Williamson’s Cabinet. 
