ON NBMATOPHYTON AND ALLIES. 37 



subsequently submitted for examination, relative to the proper structure and affinities of 

 the plant. As it is the principal object of the present examination to throw su.ch additional 

 light as may be possible upon this controversy, it may be well briefly to pass in roview 

 the leading points of the discussion. 



The original description of the pkint is as follows' : — 



" Woody and branching trunks, with concentric rings of growth and medullary rays ; 

 cells of pleurenchyma not in regular lines, cylindrical, thick-walled, with a double series 

 of spiral fibres ; discs or bordered pores few, circular and indistinct. The specimens are 

 usually silicilied, with the bark in a coaly state." 



In the text following this description, Sir Wm. Dawson expresses a doubt as to the 

 actual presence of discs, when he says that " all present cylindrical wood fibres, marked 

 with irregular spiral lines, and indications, perhaps illusory, of small, round pores placed 

 at unequal intervals. The woody hbres are of great length, but not closely in contact 

 with each other, giving to the wood a lax appearance, like that in very young coniferous 

 stems. The fibres are not placed in regular radiating series, but are divided into wedges 

 by radiating bands representing the medullary rays, and there are distinct lines of growth 

 in which the fibres are of smaller diameter than elsewhere." 



The text further states that " with the exception of the lines of growth, I have failed 

 to observe any change of structure in passing from the circumference to the centre. No 

 pith has been observed, and the bark, when present, is thin and coaly. The roots have 

 precisely the same structure with the stems, except that the fibres appear to be a little 

 larger, and with the walls less thickened. 



" In all the specimens there are evident indications of medullary rays, in radiating 

 bands and lenticular spaces traversing the wood ; biit the structure of the rays has per- 

 ished, as one frequently observes in old and weathered trunks of modern trees. This 

 would either indicate that the medullary rays were lax and perishable, or that all the 

 specimens have been much decayed before fossilization. 



" In one instance a large branch was observed to be given off, and on other trunks 

 knots, representing the attachment of small lateral branches, like those of ordinary pines, 

 were found. The most remarkable external marking consists in certain transverse swel- 

 lings, which give to the trunk an irregularly articulated appearance. These swellings are 

 connected with a gnarled appearance of the external layers of the wood, but the internal 

 layers appear smooth, as if the structure supervened in an aged condition of the trunk." 

 Although the absence of proper vascular structure is also recognised, the plant is 

 held to have a dense woody structure, and regular exogenous mode of growth. 



In his account of subsequent examinations of this fossil, Mr. Carruthers makes the 

 following statement : — 



" Under a low power, a transverse section exhibits a somewhat loosely aggregated 

 mass of circular openings of nearly uniform size, except that there are recurring tracts of 

 smaller and more closely aggregated openings. These tracts have a concentric arrange- 

 ment, and are the rings of growth of Dr. Dawson. On submitting the specimens to a 

 higher power, we find that the circular openings have well-defined walls of considerable 

 thickness, and that they are nearly uniform in size, except where the tracts of small dia- 



Geol. Surv. Can., Fossil Plants, 1S71, 16. 



