708 DR R KIDSTON AND PROF. W. H. LANG ON OLD RED SANDSTONE PLANTS. 



spherical protuberances. As figs. 11 and 12 on PI. Ill show, this has involved a 

 large number of the superficial cells, but only affects the epidermis and outer cortex. 

 The result of this is that the large bulges, like the smaller bulges on the aerial stems 

 to be described below, are growths from the superficial tissues only, and have no 

 vascular supply from the stele of the rhizome. 



The cell contents have disappeared or are unrecognisable, but no evidence of the 

 presence of a fungus forming a mycorhiza has been found, although the saprophytic 

 fungi in the peat are well preserved. 



Aerial Stem. 



The aerial stems, as already shown (PI. II, fig. 5), tapered gradually upwards, and 

 slight modifications of the structure will have to be taken into account. Moreover, 

 the lower portions of the stems must have been surrounded by the peat, and would 

 constitute an ill-defined transition region. The range in diameter of stems can be 

 seen at a glance in figs. 21-25 on PL V. These transverse sections are all of the 

 same magnification (x 20), but the largest (fig. 21 ) is of a stem of only medium 

 size, a little under 3 mm. in diameter, while stems of mm. diameter have been 

 observed. The smallest (figs. 24-25) are under 1 mm. in diameter. 



Fig. 20, PL V, shows a number of stems from the upper region of the plant 

 embedded in an almost pure silicious matrix. As the portions isolated in the round 

 show (PL III, figs. 0-8), the stem had a well-marked epidermis, was destitute of 

 leaves, but bore small hemispherical projections which were irregularly distributed. 



The sections of stems in figs. 21-25 do not pass through any of these small pro- 

 jections, but the transverse section in fig. 27, and the longitudinal section in fig. 20, 

 show them. The bulges of similar size shown in figs. 28-29 differ by bearing 

 rhizoid-like hairs. It is a reasonable supposition, though we have no direct evidence 

 for it, that these rhizoids were mainly developed in the transition region. In one 

 case, however, a rhizoid was observed on. a bulge in the upper region of a stem. 



Fig. 30 shows an aerial stem preparing for dichotomous branching. The stele 

 is already divided. 



A characteristic aerial stem of good size is shown in transverse section in fig. 21. 

 It exhibits the well-marked epidermis (ep.) with a thick outer wall and cuticle. 

 The two or three succeeding layers of clear cells form the narrow outer cortex or 

 hypoderma (o.c). The broad inner cortex (i.e.) is composed of smaller rounded cells 

 with intercellular spaces. The phloem (ph.) contrasts with the cells of the sur- 

 rounding cortex by the smaller diameter of its thin-walled elements. In the centre 

 is the solid strand of xylem (x.). The corresponding arrangement of the tissues is 

 seen in longitudinal section in fig. 20, and even more clearly on PL VIII, fig. 59. 



The several tissues may now be considered in order from without inwards. 



Epidermis and Stomata. — The appearance of the epidermis in transverse section 

 is well shown in PL VI, fig. 35, which includes portions of the outer surface of two 



