1. _Nematophycus Logani_ (Daws.). Fig. 39, A–E. The stem possesses well marked concentric rings of growth due to a periodic difference in size of the large tubular elements. The tissues consist of two distinct kinds of tubular elements, the larger tubes loosely arranged and pursuing a fairly regular longitudinal course, and having a diameter of 13–35µ; the smaller tubes, with a diameter of 5–6µ, ramify in different directions and form a loose plexus among the larger and more regularly disposed elements. Branching occurs in both kinds of tubes; septa have been recognised only in the smaller tubes. Irregular and discontinuous radial spaces traverse the stem tissues, having a superficial resemblance in their manner of occurrence to the medullary rays of the higher plants. The best specimens of this species were obtained by Sir William Dawson from the Devonian Sandstones of Gaspé in New Brunswick. The largest stems had a diameter of 3 feet and reached a length of several feet[377]; 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 one sees the concentric rings of growth clearly etched out by weathering agents in a cross section of a large stem.