Knowledge of Rachiopteris cylindrical Will . 
533 
i. Stems} 
i. General description :—An examination of the serial sections of 
R. cylindrica gives the impression of a slender plant, the stems of which 
may have been prostrate upon the ground, or semi-erect, supporting them¬ 
selves upon the surrounding vegetation. 2 These stems branched dichoto- 
mously 3 (PL XXVI, Figs. 5, 8, 9 ; Text-figs. 1, 7, 8) or produced leaves 4 
(PI. XXVI, Figs. 6 and 9 ; Text-figs. 8 and 9) at variable but fairly infre¬ 
quent intervals, so that the habit of the plant must have been somewhat 
lax. 5 (See Text-figs. 1 and 8, in which the length of stem represented is 
indicated.) The relation of leaf production to dichotomy is variable; 
usually there is an interval between the two processes, although a leaf 
may occur in close association with a branch, as shown in Text-fig. 8. 
Slender roots occur—usually singly—at or near the points of branching 
or leaf production (PL XXVI, Figs. 8 and 3). 
The stems of R. cylindrica are circular in transverse section (PL XXVI, 
Figs. 2, 3, and 4), their average diameter being from 2 to 2*5 mm. The 
single central stele possesses a cylindrical core of wood (PL XXVI, Figs. 1-4), 
surrounded by phloem, in which the sieve-tubes are often distinct (PL XXVI, 
Fig. 2; PL XXVII, Fig. 4; Text-fig. 5) ; a somewhat irregular layer of 
cells, usually darkened, separates the stelar tissues from those of the 
cortex, and may be considered as an endodermis (PL XXVI, Fig. 1 ; PL 
XXVII, Fig. 4). The wood may have a single protoxylem group 6 (Pl. 
XXVI, Figs. 2, 3, and 7), in which case the structure is centrarch, or 
typically endarch ; or there are from two to five groups (PL XXVI, Fig. 1 ;. 
PI. XXVII, Fig. 4 ; Text-fig. 2), when the structure tends towards mesarchy, 
1 For previous references see— 
Williamson (’ 78 ), pp. 550, 351 ; PI. 24, Figs. 80-88. 
Hick, T. : On Rachiopteris cylindrica , Will. Mem. and Proc. Manchester Lit. and Phil. 
Soc., vol. 41, 1896, p. 1, PI. I. 
Tansley, A. G. : Lectures on the Evolution of the Filicinean Vascular System. New Phyt., 
Reprint, 1908. See p. 14 and Fig. 4. 
Browne, Isabel: The Phylogeny and Inter-relationships of the Pteridophyta. New Phyt., 
Reprint, 1908. See p. 57. 
Scott, D. H. : Studies in Fossil Botany. Second Edition, 1908. See p. 333. 
Seward, A. C. : Fossil Plants, vol. 2, 1910. See pp. 438-40 and Fig. 305. 
2 See p. 554. 
3 This term is used provisionally and in a purely descriptive sense; as Dr. Lang has pointed out to 
the writer, it may be necessary to modify our views with regard to apparent dichotomy in these forms. 
4 Throughout the following account, the acropetal method of description is adopted, as being, in 
this case, the most convenient; see Boodle, L. A. : On Descriptions of Vascular Structures. New 
Phyt., vol. 2, 1903, p. 107. This author justifies the use of the acropetal method in descriptions of 
‘ ferns, which have a solid cauline stele, or in which there are no leaf-traces showing distinct 
individuality in the internode ’, for ‘ in this way it is clearly seen what part of the stele is continuous 
with the leaf-trace ’ (p. 108). 
5 Tansley (’ 08 ), p. 15 ; Scott (’ 08 ), p. 333. 
6 That is, a group of small elements suggesting protoxylem; they do not seem to possess the 
typical annular or spiral thickenings. 
