20 PENHALLOW ON 



septate, and more recent examinations have shown so many vindoubted instances of 

 branching — as may be seen in the figure — that the relationship to N. Logani cannot be 

 questioned. 



As stated in my former paper, these larger cells have a diameter of 12 - 22 //, but as this 

 applies only to the siliceous casts, we must add to this, assuming the walls to be of the same 

 thickness as in N. Logani, 10.5 //, which would make the total diameter of the original 

 cells 31.5 //, or equal to some of the larger cells of N. Logani. 



A secondary system of filaments is also evidently present. Casts of small tubular 

 cells are very frequent. They have a diameter ranging from 1 to 1.5 //. Together with 

 these there are also casts of branching filaments, many of which have free terminations 

 and exactly resemble the young hypha? of a fungus. These latter were in all probability 

 derived from a fungus growing in the plant as a feature of its decay. The fact, however, 

 that the larger cells of the medulla branch, permits me to consider that some of the casts, 

 at least, belonged to a secondary plexus of filaments which were in all essential respects 

 the same as in N. Logani or N. laxum. 



Spores are abundant. These bodies are of a reddish-brown color, measure 1.58 /< in 

 diameter and are often aggregated into dense, spherical masses of reddish brown, resinous 

 looking substance. To this I would refer the spherical masses of a similar character 

 already noted as occurring in both N. Logani and N. crassum, and it seems highly probable 

 that they were derived, in each case, from associated fungi. 



The fine striation or transverse marking on the casts, as originally pointed out by 

 Mr. Etheridge,' has been noted by me in more than one case. It is not, however, a constant 

 feature, bn.t occurs only now and then. If such marking represented stru.cture in the cell 

 wall, we might reasonably expect to find it, if not on the casts of all the cells, at least on 

 so many of them as to leave no doubt in ovir minds relative to its proper connection. On 

 the other hand, such markings are distinct from the ordinary striation of the cell wall and 

 their position is variable. They resemble in fact markings made upon the casts by pres- 

 sure of some external structure exerted throitgh the cell wall. In my last communication 

 on this plant," I expressed a doubt as to these markings representing any structure in the 

 cell wall, and from more recent examinations I do not hesitate to express the belief that 

 that they are in reality caused by the filaments of the intercelhtlar plexus. 



From the facts stated above, it would appear that there is ample reason for confirm- 

 ing the position already assigned to this plant. It may be only another condition of N. 

 Logani; but this, in view of the highly altered nature of the specimens so far obtained, 

 cannot be definitely affirmed, and for the present, therefore, it miast necessarily remain 

 under its present specific name. 



Nematoxylon crassum, Dn. 



The original description of this plant is as follows ' : — 



" Fragments of wood with a smooth, thin bark and a tissue wholly composed of 

 elongated cylindrical cells with irregular pores or markings. No pith, medullary rays, nor 

 rings of growth." 



' Quart. Jn'I. Geol. Soc, Aug., 1881, 492 ; fig. 4. - Trans. B. S, C, vi. iv. io. 



» Quart. .Tn'l. Geol. Soc, Nov., 1863, 466. 



