DEVONIAN PLANTS. 23 



to as associated with N. Logani. Their exact nature remains doubtful. They are usually 

 found disposed in the cell in linear series of two to twelve or more. They are in all cases 

 quite distinct from the cell wall. Bodies of the same kind have also been seen, though 

 less frequently, in N. Logani, and abundantly in N. Hicksii, where they are obviously coin- 

 posed of pores. 



From the above it is evident that our plant is a Nemaphyton, though it differs from 

 N. Logani in important respects. It approaches more nearly to N. laxiun, but again differs 

 from it in its more compact structure, greater uniformity of size in its cells, and in its less 

 prominent intercellular plexus. We may, therefore, regard it as a distinct species for 

 which I would retain the name crassum as properly descriptive. 



A revised description would be as follows : — 



Nematophyton crassum, Pen. 

 Nematoxylon crassum, Dn. 



Growth rings (?), pith and radial tracts none. The plant wholly composed of 

 thin-walled, structureless, vermicular and non-septate cells which branch into a 

 secondary plexus. Open tracts frequent, and of irregular size, in which the branch- 

 ing chiefly occurs. Cells of the medulla rather uniform and thick walled — wall 

 double — 35 /< in diameter. Cells of the hyphal structure variable, from 2 /; to 10 /< 

 in diameter. 



Specimens found only in fragments. From the Middle Brian of Gaspé. 



CeLLULOXLYON PRIM..EVUM, Dn. 



In the course of my examinations of Nematophyton during the past two years, certain 

 peculiarities of structure due to alteration in the distribution of the organic matter attracted 

 attention, and suggested their possible identity with the structure of certain fossils 

 already brought to my notice by Sir Wm. Dawson, under the name of CeUuloxijlon 

 primœvum. These latter have therefore been subjected to a more critical examination with 

 a view of determining if they are in reality distinct species, or merely altered forms of 

 some other plant. As a preliminary to this examination, I may detail the peculiarities 

 of structiire in Nematophyton above referred to. 



Nematophyton. 



In most of the specimens of Nematophyton examined by me, the tubular character of 

 the cells is so perfectly preserved as to admit of no doubt concerning their correct form and 

 size. In section taken from very highly silicified and crystalline specimens, however, it 

 is found that the infiltrated silica has often so far replaced the organic matter as to leave 

 not the faintest trace of cellular structure, and very frequently no trace of organic matter. 

 In other specimens, various intermediate stages of silification are to be observed in which 

 both organic matter and cellular structure are more or less conspicuous, but of an 

 obviously altered character. In many cases it has been found that the infiltration of 

 siliceous matter, under certain conditions, has resulted in its deposition in a distinctly 

 crystalline form which fills the tubular cells throughout. In all such cases I have 



