608 DR R. KIDSTON AND PROF. W. H. LANG ON OLD RED SANDSTONE PLANTS 
also associated with the typical stems of this species, in some specimens of the 
silicified peat collected from the section exposed in situ. 
The stems of R. major must be more fully described, since the description of the 
stem of Rliynia in Part I was almost entirely based on specimens of R. Gwynne- 
Vaughani. 
As regards size, the examination of large numbers of sections of stems has shown 
that in R. major a diameter of 5-6 mm. was often attained (PI. II, figs. 14, 19). 
Finer branches, probably from the upper region of the plant, are met with down 
to a diameter of 1‘5 mm. or less (fig. 15). These measurements contrast with those 
of R. Givynne-Vaughani, in which the usual diameter of larger stems is about 2 mm., 
though a thickness of over 3 mm. is sometimes attained, while the finer stems or 
branches may be less than 1 mm. in diameter. 
On PI. Y of Part I two transverse sections of R. major were figured in figs. 21 
and 22. Large as they appear in comparison with the other stems on the same 
plate, the difference is in reality greater, since their magnification should have been 
given as x 14 instead of x 20. A true comparison with the stems of R. Gwynne- 
Vaughani, magnified 20 diameters, in Part I, PI. V, figs. 23-29, is afforded by the 
accompanying figs. 14, 19, 17, and 15 on PI. II of this memoir. 
A general view of a portion of the silicified peat composed of large stems and 
sporangia of R. major is given at a lower magnification ( x 7) in PI. Ill, fig. 25. The 
stems shown in figs. 18 and 21 are magnified 14 diameters. 
All these figures show how closely the stem of R. major agrees in general 
construction with that of R. Givynne- Vaughani* As is best shown in the well- 
preserved stem in fig. 14, there is a clear differentiation into epidermis ( ep .), outer 
cortex (o.c.), inner cortex ( i.c .), phloem (ph.), and xylem ( x .). A difference that 
may be at once emphasised is the absence of the hemispherical projections which 
are such a striking feature of many stems' of R. Gwynne-Vaughani. In the large 
number of sections of R. major examined no trace either of hemispherical pro- 
jections or of the adventitious branches corresponding in place of origin to them 
has been seen. 
The epidermis had the outer walls thickened and covered with a well-marked 
cuticle. It appears smooth, and no ridges have been observed on the epidermal cells. 
Stomata were sparingly present as in R. Gwynne-Vaughani. The outer cortex, two 
or three cells deep, was evidently a mechanically important hypoderma in the larger 
stems. Within it came the wide inner cortex, the outer cells of which, when well 
preserved, often have the dark contents common in the same position in R. Gwynne- 
Vaughani (fig. 14). The outer cortex was interrupted beneath the stomata, as is 
shown in figs. 14 and 18 and in Part I, PI. VI, fig. 37. In the large stems the outer 
cortex was very resistant to decay, while the wide inner cortex often broke down 
(figs. 25, 19, 18). 
* This is also brought out in comparing figs. 21 and 22 with the other figures on PI. V of Pt. I. 
