1 68 Gibson . — Contributions towards a Knowledge 
The xylcm presents the anomaly of having its metaxylem 
partly, at least, composed of scalariform tracheae (vessels), the 
transverse walls being wholly (or sometimes only partially) ab- 
sorbed (PI. XII, Fig. hi). The trabeculae are of the usual type. 
34 . Selaginella rupestris , Spr. Baker’s Handbook, No. 6 . 
This species approaches very closely in the anatomical 
structure of the stem to X. oregana. The stele is single 
throughout, and has all the leaf-traces inserted on the marginal 
protoxylems. A dorsal cord is formed as in the typical 
monostelic forms, which soon fuses with the marginal proto- 
xylem of the side on which the branch arose. The leaf-traces 
are very long, and those which belong to leaves not inserted 
opposite the margins of the stele curve round, partly in the 
cortex, partly in the pericycle, to be likewise inserted on the 
marginal protoxylems. 
There is a large development of sclerenchyma which 
envelopes the swollen bases of the leaves ; it does not, how- 
ever, exist as an isolated internal annulus as figured and 
described by Dangeard ( 22 ). The inner cortex is small in 
amount and loosely arranged, trabeculae of the usual type 
connecting it with the stele. In any given section ten leaf- 
traces are seen, five within and five alternate with these 
outside. In Dangeard’s figure seven leaf-traces are shown in 
the cortex, although he states, on the authority of A. Braun, 
that the phyllotaxis is a spiral. 
The stele consists of a pericycle of three to four layers of 
large cells— not one, as represented by Dangeard — and one 
interrupted layer of very small angular sieve-tubes, quite 
absent opposite the marginal protoxylems. Like 5. oregana 
the metaxylem consists of distinct tracheae. Dangeard’s 
figure of the course of the leaf-traces (22. PI. X, Fig. 4 ) repre- 
sents nothing that I am acquainted with in the anatomy of 
the species. 
C. Anomalous Monostelic Species . 
I now propose to give a brief account of two species, one 
of which, X. Braunii , Baker, may be associated with species of 
