VIl] NEMATOPHYCUS. 195 



The best specimens of this species were obtained by Sir 

 William Dawson from the Devonian Sandstones of Gasp6 in 

 New Brunswick. The largest stems had a diameter of 3 feet 

 and reached a length of several feet' ; in some examples 

 Dawson found lateral appendages attached to the stem which 

 he described as "spreading roots." Externally the specimens 

 were occasionally covered with a layer of friable coal, and 

 internally the tissues were found to be more or less perfectly 

 preserved by the infiltration of a siliceous solution. Most of 

 the examples of Nematophycus from Britain and Germany are 

 much smaller and less perfectly preserved than those from 

 Canada. The Peter Redpath Museum, Montreal, contains 

 several very large blocks of Nematophycus, in many of which 

 d^e sees the concentric rings of growth clearly etched out by 

 weathering agents in a cross section of a large stem. 



In fig. 39, A, a sketch is given of a thin transverse section of 

 a stem, drawn natural size. The lines of growth are clearly 

 seen, and as in coniferous stems the breadth of the concentric 

 zones varies considerably. The short lines traversing the 

 tissues in a radial direction represent the medullary-ray-like 

 spaces referred to in the specific diagnosis. A transverse section 

 examined under a low-power objective presents the appearance 

 of a number of thick-walled and comparatively wide tubes 

 loosely arranged; they may be in contact or separated from 

 one another. If the microscope be carefully focussed through the 

 thickness of the section the transversely-cut tubes appear to move 

 laterally, producing a curiously dazzling effect if the objective 

 is raised or lowered rapidly. This lateral movement is due 

 to the undulating vertical course of the tubes. Under a 

 higher power the lighter-coloured matrix in which the tubes 

 are embedded shows a number of very much smaller and 

 thinner- walled hyphal elements; some of these are cut across 

 transversely, others more or less obliquely and others again 

 longitudinally. These smaller tubes constitute an irregular 

 plexus surrounding and ramifying between the larger elements. 

 The diameter of the larger tubes decreases for a certain 

 distance in a radial direction as seen in a transverse section, 

 1 Dawson (59), also (71) p. 17. 



13—2 



