382 MR. W. N, EDWARDS ON THE 
Comparisons with other Specimens. 
In comparing the present material with previously described examples of 
P. princeps we naturally consider first Dawson's figures and descriptions. 
Weare not here specially concerned with the plant as a whole nor with its 
supposed rhizomes and fructifieations, but in order to give a clear idea of the 
external appearance of the stems as they occur at Gaspé one of Dawson’s 
specimens is reproduced on Pl. 37. This is the slab (or possibly its counter- 
part) partly figured by Dawson (1571)on pl. 9. fig. 97. It may be noted that 
in his drawing the spines are occasionally shown as rather stouter structures 
than is justified by the appearance of the actual specimen. The longest piece 
of stem I have seen (incomplete at each end) is 18 cms., and the British 
Museum specimens do not exceed 5 mm. in breadth, except at the point of 
branching. Dawson states (1871, p. 39) that “after the removal of the 
leaves the stems exhibited rounded spots somewhat irregularly arranged, 
indicating the slender bundles of vessels passing to each leaf." The minute 
spine scars do not seem to me, however, to warrant the statement that 
vascular bundles ran out to the **leaves." When the actual cuticle is present 
the sears are often merely round or oval lacunæ, and in the casts there is 
usually only a little tubercle to be seen (or a depression in the case of moulds, 
sometimes filled with a fragment of cuticle which thus makes a black spot on 
the impression), and I have not observed any central spot which might be 
interpreted as a vein-scar. 
Dawson does not mention stomata in his description, but figures (1871, 
pl. 11. fig. 1294) a “portion [of a leaf] more magnified, showing cellular 
structure and a stoma.” There is nothing in the drawing, unfortunately, 
which bears any particular resemblance to a stoma, and as stated above I have 
not been able to confirm the presence of stomata on the spines, 
The species has been recorded from various localities, and among the figures 
given by Halle (1916) of material from Norway are two (pl. 2. figs. 3 & 5), 
“sculpture of the outer surface” which Halle tentatively regards 
as representing the epidermal cells. A comparison with the cuticle described 
in the present paper confirms this, and the average breadth of the cells is the 
same in each case. The stems of the Norwegian specimens are larger than 
the Canadian material in the British Museum, sometimes having a di: ter 
of 10 mm., but the spines are about the same size. a diameter 
A specimen of P. princeps from the Lower Old Red Sandstone of Perth- 
shire, has recently been figured by Mr. J. Walton (1923, pl. 9. fig. 12) in 
illustration of his new method of preparing fossil plants. His specimen shows 
the spines very clearly but not the cellular structure of the epidermis. 
Since the spines were better preserved than the rest of the plant, Walton 
concludes that they were more highly eutieularised, and suggests that * they 
were probably not structures representing an extension of the area of 
protosynthetie tissue, and that if they had any function at all it was of a 
showing a 
