ON NEMATOPHYTON AND ALLIES. 41 



twice or thrice iu the same layer. This appears in Plate I, fig. 2, where, to the left of the 

 principal radial opening, a very short and detached area is seen to traverse only the 

 smaller-c('lh'd tissue. A similar short opening is shown in longitudinal section in Plate I, 

 fig. 4, the entire oi^ening being brought within the limit of the figure. This shows 

 that these open areas arise independently, and also that they i^nrsiie a very sinuous course 

 with reference to the horizontal plane. Nor do they bear that constant relation to one 

 another which might be looked for in true medullary rays. They frequently approach 

 one another at a very considerable angle, and also show internal variations which it would 

 be exceedingly diflicult to account for in triie rays upon any other ground than that of 

 very advanced decay. Nor are these conditions of stru.cture which can be satisfactorily 

 explained on the ground of alteration through compression and other changes attendant 

 upon the process of silicification. 



In their internal structure, the " rays " show no evidence of cellular tissue. They 

 are, on the other hand, irregularly elongated openings (Plate I, fig. 3), the central area of 

 which is traversed in all directions by a felted mass of myceloid filaments of variable size. 

 Very frequently, also, the large, tubular cells of the principal structure traverse these 

 areas iu all directions, and, in fact, it appears that i,t is in the immediate vicinity of these 

 openings, into which they ultimately turn, that the principal cells take a direction 

 obliquely or transversely to the axis of growth. In tangential section, these radial open- 

 ings appear as channels of irregularly rounded form and size, without any regularity of 

 disposition. The peculiarities of structure here indicated are clearly exhibited in Plate 

 II, figs. 5 and 6, Plate I, fig. 3. 



More recently, we have made a critical examination of the " node," as found in speci- 

 men No. 5, with the following results : — 



The joint extends entirely across the stem in such a way that the removal of any 

 part on either side exposes a flat face bearing a thin layer of a coaly, black substance. 

 This leads us to infer one of two things, \vz.., that the joint represents a distinct trans- 

 verse fracture, modified by longitudinal compression ; or that at this part of the stem there 

 was originally a distinct septum, siibsequently converted into a layer of coal, and its 

 structure thus obliterated. Carefully ijrepared transverse and longitudinal sections 

 passing through this particular part of the structure, were examined for any additional 

 explanation they might aflbrd. The former exhibited nothing which could be regarded as 

 different from the structure in other x^arts of the stem. In the longitudinal section, the 

 cells were, in some cases found to be more loosely disposed than elsewhere, and possibly 

 exhibited a greater tendency to interlace, but in neither respect was the difference so 

 marked as to enable us to regard it as peculiar to that particular part of the stem. So far 

 as anything was indicated, it was that this region of the structure had sustained the full 

 force of longitudinal compression, which thereby caused an external swelling of the trunk, 

 with corresponding opening of the interior structure. This would harmonize with the 

 appearance described by Sir "Wm. Dawson. Moreover, along the entire face of the frac- 

 ture, the cells were found to be all abruptly cut off, thus showing that instead of repre- 

 senting any peculiar structural feature, the joint is in reality a transverse fracture of the 

 stem. The narrow opening thus formed eventually became filled with infiltrated mate- 

 rial, and to a more limited extent with organic matter derived from the decay of the 

 adjacent surfaces. In this we doubtless have a correct explanation of the amorphous coal 



Sec. IV, 1888. 6. 



