along the radial longitudinal planes in the wood, exhibiting the grain of the wood on the fractured surfaces. It also breaks along cylindrical surfaces which are approximately coincident with the surfaces of the late wood of the growth rings. The pith is not preserved.

In one incomplete transverse section cut from the specimen, one can detect on careful examination the presence of two of the rings of late wood; each is followed abruptly by large early-wood elements. The change from early to late wood is gradual, and the tracheids of the late wood may measure as little as 16μ, and those of the early wood as much as 50μ (av. 45μ) in radial diameter. The growth rings are 2 mm., 10 mm., 13 mm., and 13 mm. broad respectively, the 2-mm. ring being next to the pith. The tracheids are square to rectangular, and are in very regular radial files, separated by not very frequent rays. In radial section it is evident from the frequency with which the sharply tapered ends of tracheids occur that the tracheids are rather shorter than in most gymnospermous woods.* The medullary rays are somewhat few in number, and are seen to be from 1 to 8 cells high. In tangential section they are seen to be uniseriate. In sections cut from this specimen none of the finer structures can be made out, as the walls of the cells are covered with a granular crystalline deposit. It is possible, however, to get a good idea of the radial structure of the cell walls by examination of the fractured surfaces.

The radial walls of the tracheids have numerous bordered pits arranged in one to three series; these pits were contiguous and probably slightly flattened. I have not seen areas of tracheid wall without pits. The diameter of the pits is approximately 10μ, which is the average of measurements from several contiguous series of pits. The tracheids are often seen with their tapering ends curved in the radial plane so that the terminal portion of each is in contact with several tracheids in the adjacent files (cf. D. arberi, Sew., Arber, 1905, text-fig. 42). In Rhexoxylon africanum, the secondary wood of which was examined in radial fracture, the tracheids are not curved at their ends to such an extent.†

Specimen. Cat. No. 2946 S.A. Mus.

Locality. Near Noro Kei Pan, Gordonia (Bechuanaland, Cape Province). Horizon.

Base of Ecca or Upper Dwyka Shales (Lower Permian).

* Arber, 1905. Cf. "Dadoxylon australe," Arber, p. 192, and text-fig. 42.

Phyllocladoxylon capense, sp. nov.

(Pl. III, figs. 17, 18.)

The specimen (No. 1950, Albany Museum), of which only three sections were available for examination by the writer, consists of secondary wood only. It is riddled with borings which run in a longitudinal direction in the wood. Distinct growth rings are present, and are of the stem-wood type. The rings are clearly composite (Pl. III, fig. 17). In transverse section the medullary rays are seen to be uniseriate, and no wood parenchyma is evident. The rays cells are represented by a black substance in the lumen of the original cells, the walls of which have generally disappeared.

In longitudinal section structures, which must be interpreted as resin plates, can be seen in the tracheids. No septate tracheids or wood parenchyma is represented in any of the sections. The tracheids are pitted on the radial walls, only occasionally can a small bordered pit be found on the tangential wall of a late formed element of a ring. The bordered pits are elliptical, with the major axis of the ellipse at right angles to the long axis of the tracheid. They may be arranged widely separated in single file or may be contiguous. A biseriate arrangement is also a regular feature of this wood, and then the pits may be either opposite or alternate, but not usually flattened by contact. In the wider spring elements the pits are usually about 14μ×20μ, while in the late wood, and even in the early wood, they may be approximately circular and 9μ in diameter. This variability in the size of the tracheid pits is one of the distinctive characteristics of this wood. The breadths of the tracheids seen in transverse section are about 35μ (max. 45μ) radially and 50μ tangentially in the early wood, and in the late wood may be as little as 20μ radially.

The medullary rays are uniseriate and vary from 1 to 18 cells in height, that of a single cell being from 22μ to 25μ. In radial section the field pitting is seen to consist of a large simple pit filling the field almost completely (Pl. III, fig. 18). The walls of the ray cells are not preserved, and must have been considerably thinner than those of the tracheids. The large pit seen in the field is the pit in the wall of the tracheid; and this is confirmed by comparison with what is seen in tangential section. The pit in the field is usually elliptical with the long axis horizontal. The axis length in a large pit may be as much as 40μ, the vertical axis being 13μ. In the late wood the corresponding pit dimensions may be 17μx 9μ. The absence of a

VOL. XXII, PART 1.

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border is probably an original feature. Fungus mycelium is present in some parts of the wood.

I have used the generic form name, Phyllocladoxylon, Gothan although objections to its use have been raised because of the difficulty of distinguishing between Podocarpoxylon and Phyllocladoxylon.* The field pitting in some members of the Podocarpoxylon group is variable; the same wood having in some parts of the rays bordered pits in the field, and at others simple pits. There is no indication of variability in this species, and although the name Phyllocladoxylon may be said to be rather misleading, the description originally given with the name is quite clear.† This species differs from woods included in Xenoxylon in having much smaller pits in the tracheids.

This specimen is unlike previously described Phyllocladoxyla in the size of its field pitting. The specific name capense is proposed for fossil wood possessing the characters enumerated above. It is the first of its form-genus to be found in South Africa.

Horizon. Unknown (Cretaceous or Tertiary ?).
Locality. Sunday River, Cape (Dr. Atherstone).

Spiroxylon Africanum, sp. et gen. nov.

(Pl. II, fig. 12, and Pl. III, figs. 15, 16.)

An interesting specimen (No. 2945, S.A. Mus.) from the neighbourhood of Arms Fontein, of unknown horizon, exhibits a type of secondary wood structure very similar in some respects to that of the Taxoideae, Pilger. The preservation is good, but unfortunately only the secondary wood is represented.

In transverse section growth zones are clearly distinguishable, but on examination under the microscope these are seen to be rather ill-defined. There is no sharp change in dimensions from the tracheids of the summer-formed wood to those of the succeeding spring wood. The average breadth of a growth zone is about 7 mm. The diameters of the tracheids, radial and tangential, are, for the spring wood, 33μ×26μ, and for the summer wood, 26μ×24μ respectively. In tangential section the medullary rays are seen to be almost entirely uniseriate and to vary from 1 to 18 cells in height. The tracheids in all longitudinal sections are seen to have spiral thickening bands

*Seward, 1919, p. 203.

† Gothan, 1905, p. 47, fig. 8d.

Pilger, 1903. Groups Taxus, Cephalotaxus, and Torreya in the Taxoideae.

(Spiralverdickung *) in addition to the normal secondary wall thickening. These bands in size bear the same relation to the tracheid as do those in the living genus Taxus. There may be one or two of these bands present, and in the latter arrangement a change to the single condition may be effected by a concurrence of the bands. Bordered pits have not been observed in the tangential walls of the tracheids. In radial section the rays, as can also be observed in tangential section, are composed of comparatively thin-walled cells. The dimensions of the average ray cell are 31μ and 180μ vertically and radially respectively. Occasionally the radial measurement may reach 220μ. There are two to eight small pits in the field. No border can be seen to the pits, though it is possible that a border may have been present. Pits have not been observed on the other walls of the medullary ray cells. The pitting in the tracheids consists of a single series of bordered pits (diameter 13 approx.) in contact and slightly compressed vertically. Occasionally the pits are in two series, when they usually alternate, though instances have been observed in which they are opposite. Some pits are seen to contain a dark central structure which may represent a torus.

The spiral bands pass over the wall between the pits, and do not, as far as can be seen, pass across the border in any example. This presence of bands crossing over the surface of the wall between pits makes it impossible to be certain whether Sanio's rims are present in the primary wall or not.

No resin canals or wood parenchyma have been observed in any of the sections of this specimen.

COMPARISON WITH OTHER FOSSIL WOODS.

The presence of spiral thickenings in the tracheids at once limits the number of fossil woods with which this specimen can be compared. According to Gothan † and Seward many of the fossils which have been described as possessing spiral bands in the tracheids are in a state of preservation in which partial disorganisation has caused the fibrillar structure of the cell's wall, normally invisible, to become evident. Thus the spiral thickenings in Taxoxylon Philpii, Shirley,§ are certainly due to disorganisation, as the sections figured show unmistakably. Taxoxylon scalariforme, Goepp. sp., is one of

* Gothan, 1905, p. 54.
Seward, 1919, pp. 202–203.

† Ibid., pp. 96-97.

§ Shirley, 1902, p. 15, pls. x and xi.

the fossils which probably has true spiral-thickening bands in addition to bordered pitting in the secondary wood. Gothan * states definitely that Taxoxylon scalariforme, Goepp. sp., stands as the earliest fossil record of the Taxalean type of spiral thickening. It differs mainly from the South African specimen in having the pits in the tracheids distant instead of in contact. Taxoxylon scalariforme, Goepp. sp., is of Tertiary Age.

Among the collection of fossil woods in the British Museum is a specimen (Dadoxylon sp., sections 12637-8-9) of what may be termed a Dadoxylon with quite unmistakable spiral thickening, in addition to the normal secondary wall thickening with bordered pits, in certain zones of the wood. The specimen is stated to come from the Ecca Shales, Intombi Camp, Ladysmith.

The Taxoideae, Pilger,† are the only gymnospermous group of genera which has similar spiral thickening as a constant feature of the secondary wood tracheids. Among the Coniferae, however, spiral thickening in the secondary wood is occasionally found. Thus Gothan, Bailey,§ and others || have mentioned the presence of these structures in the Abietineae, and in other groups. Spiral thickening is a constant feature in Pseudotsuga, and is usually present in the late wood of the first few years' growth of Picea and Larix. These three genera have, however, Abietinean pitting.

The nature of the "spiral-thickening bands" is not the same in the three genera of the Taxoideae; in Taxus, to which the fossil shows the closest parallel in this respect, the bands are in the form of spirals which are usually confined to the wall between the pits, but may occasionally pass across the border; in Cephalotaxus the bands may be placed so far over the border of the pits that they become tangential to the margin of the pore; and in Torreya sp., in some sections examined the arrangement is even more complicated, for the bands are sometimes in pairs, and one member of the pair may be thinner than the other, and may terminate at the margin of the pore. The main points of difference are most conveniently shown in tabulation.