Several species of Flysch Algae have recently been referred by Rothpletz[367] to the Phaeophyceae under the provisional generic name Phycopsis, but they are of no special botanical interest.
The extremely interesting genus Nematophycus has lately been assigned by a Canadian author[368] to a position in the Phaeophyceae. Although the particular points on which he chiefly relies are not perhaps thoroughly established, there are certain considerations which lead us to include Nematophycus as a doubtful member of the present group of algae.
Nematophycus.
The stem attains a diameter of between 2 and 3 feet in the largest specimens; it is made up either of comparatively wide and loosely arranged tubes pursuing a slightly irregular vertical course accompanied by a plexus of much narrower tubes, or of tubes varying in diameter but not divisible into two distinct types. Rings of growth occur in some forms but not in others. Radially elongated or isodiametric spaces occur in the stem tissues in which the tubes are less abundant.
Reproductive organs unknown, with the possible exception of some very doubtful bodies described as spores.
In 1856 Sir William Dawson proposed the generic name Prototaxites for some large silicified trunks discovered in the Lower and Middle Devonian rocks of Canada. A few years later the same writer[369] published a detailed account of the new fossils and arrived at the conclusion that the Devonian stem showed definite points of affinity with the recent genus Taxus, and the generic name suggests that he regarded it as the type of Coniferous trees belonging to the sub-family Taxineae. The reasons for this determination were afterwards shown by Carruthers to be erroneous. Dawson thought he recognised pits and spiral thickenings in the walls of the tubular elements, as well as pointed ends in some of the latter. The spiral markings were in reality small hyphal tubes passing obliquely across the face of the wider tubes, and the apparent ends of the supposed tracheids were deceptive appearances due to the fact that the tubes had in some cases been cut through in an oblique direction. In 1870 Carruthers[370] expressed the opinion that Dawson’s Prototaxites was a “colossal fossil seaweed” and not a coniferous plant. The same author[371] in 1872 published a full and able account of the genus, and conclusively proved that Prototaxites could not be accepted as a Phanerogam; he brought forward almost convincing evidence in favour of including the genus among the algae. The name Prototaxites was now changed for that of Nematophycus. Carruthers compares the rings of growth in the fossil stems with those in the large Antarctic Lessonia stems, but he regards the histological characters as pointing to the Siphoneae as the most likely group of recent algae in which to include the Palaeozoic genus.
We may pass over various notes and additional contributions by Dawson, who did not admit the corrections to his original descriptions which Carruthers’ work supplied. In 1889 an important memoir appeared by Penhallow[372] of Montreal in which he confirmed Carruthers’ decision as to the algal nature of Prototaxites; he contributed some new facts to the previous account by Carruthers, and expressed himself in favour of regarding the fossil plant as a near ally of the recent Laminariae. The next addition to our botanical knowledge of this genus was made by Barber[373] who described a new specific type of Nematophycus—N. Storriei—found by Storrie in beds of Wenlock limestone age near Cardiff. Solms-Laubach[374], in a recent memoir on Devonian plants, recorded the occurrence of another species of this genus in Middle Devonian rocks near Gräfrath on the Lower Rhine. Lastly Penhallow[375], in describing a new species, lays stress on the resemblance of some of the tubular elements in the stem to the sieve-hyphae of the recent seaweeds Macrocystis and Laminaria. He concludes that the new facts he records make it clear that Nematophycus “is an alga, and of an alliance with the Laminarias.” The recent evidence brought forward by Penhallow is not entirely satisfactory; the drawings and descriptions of the supposed trumpet-shaped sieve-hyphae are not conclusive. On the whole it is probably the better course to speak of Nematophycus as a possible ally of the brown algae rather than as an extinct type of the Siphoneae, but until our knowledge is more complete it is practically impossible to decide the exact position of this Siluro-Devonian genus.
Solms-Laubach[376] has suggested that the generic name Nematophyton, used by Penhallow in preference to Carruthers’ term Nematophycus, is the more suitable as being a neutral designation and not one which assumes a definite botanical position. In view of the nature of the evidence in favour of the algal affinities of the fossil, the reasons for discarding Carruthers’ original name are hardly sufficient.
Before discussing more fully the distribution and botanical position of Nematophycus we may describe at length one of the best known species, and give a short account of some other forms.
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