2. Nematophycus Storriei Barber. Fig. 40. The specimens on which Barber[382] founded this species were obtained by Mr Storrie from the Tymawr quarry near Cardiff, in beds of Wenlock age. The fragmentary nature of the material is largely compensated for by the excellence of the preservation. We may briefly define the species as follows:
The stem consists of separate interlacing undivided and usually unbranched tubes of varying diameter. Spaces more or less isodiametric in dimensions are scattered through the tissue. The spaces constitute regions in which the tubular elements branch freely.
The main distinguishing features of this British species are (i) the absence of two distinct and well-defined forms of tubular elements. The main part of the stem consists of thick walled tubes similar to those of N. Logani, but the spaces between them are occupied by thinner-walled and smaller tubes varying considerably in diameter; (ii) the form of the spaces which are not radially elongated as in N. Logani.
Fig. 40. Nematophycus Storriei Barb. Longitudinal section, from a photograph by Mr C. A. Barber. × 45.
Fig. 40 shows the undulating course of the tubes as seen in a longitudinal section; the black colour of some of the elements is due to the fact that the surface of the wall is seen, while in the lighter-coloured portions of the tubes the wall has been cut through. The lighter patch about the middle of the figure shows the form of one of the spaces in which the tubes are freely branched.
In addition to the two species already described six others have been recorded, but with these we need not concern ourselves in detail. One of these species, N. Hicksi, was found by Dr Hicks[383] in the Denbighshire grits quarry of Pen-y-Glog near Corwen in North Wales. The position of these beds has recently been determined by Mr Lake[384] as corresponding to that of the Wenlock limestone. This species and N. Storriei are both Silurian examples of the genus. It is possible, as Barber has suggested, that the specimens described under these two names should be referred to one species. The specimens found by Hicks were small and imperfectly preserved fragments; Etheridge has given a full description of their structure, and Barber has subsequently examined the material. The preservation is not such as will admit of any very precise specific diagnosis; the fragments are correctly referred to Nematophycus, but their specific characters cannot be clearly determined.
Solms-Laubach[385] has described some fragments of another species of Nematophycus from the Devonian rocks of the Lower Rhine. His specimens are chiefly interesting as extending the geographical range of the genus, and as affording examples of a curious method of preservation. The specimens obtained were small fragments, flattened and very dark brown in colour. The tubular elements consisted of an external membrane of black coal, enclosing a central core of dark red iron-oxide. On burning the fragment on a piece of platinum foil the coal composing the wall of the tubes was removed and the deep-red casts of the tube-cavities remained[386]. The investigation of the structural characters of this imperfect material was conducted by reflected light. Under certain conditions, when it is impossible to obtain thin sections for examination by transmitted light, it is possible to accomplish much, as shown by Solms-Laubach’s work, by means of observation with direct light.
The last species to be noticed is Nematophycus Ortoni recently described by Penhallow. There are no concentric rings of growth, no radial spaces and no smaller hyphae in the tissues of this type of stem. In longitudinal section, the tubes show occasional local expansions of the lumen which Penhallow compares with the ‘trumpet-hyphae’ of some recent brown algae. No actual sieve-plates or transverse walls have been detected, but the general appearance of the tubes is considered to afford distinct evidence of the original existence of such walls. The figures accompanying the description do not carry conviction as to the correctness of the reference of the tubes to imperfectly preserved sieve-hyphae.
The following list, taken, with a few alterations, from Penhallow’s memoir[387], shows the geographical and geological range of the species of Nematophycus hitherto recorded.