SHOWING STRUCTURE, FROM THE RHYNIE CHERT BED, ABERDEENSHIRE. 835 
Rliynia major (PL I, fig. 2). 
In the case of this plant there is no direct indication as to height or habit. All 
parts of the plant, however, are known and are distinctly larger than the correspond- 
ing parts of Rliynia Gwynne-Vaughani. The diameter of the cylindrical stems 
ranged from 5 or 6 mm. to under 1‘5 mm. The stems are known to have branched 
dichotomously, and doubtless tapered as in the case of the smaller species. In the 
reconstruction we have represented the plant as about three times the height of 
R. Gwynne-Vaughani. The sporangia are known to have terminated some of the 
slender axes about 1'5 to 2 mm. in diameter. They attained the large size of 
12 mm. x 4 mm. Sometimes two sporangia lay side by side in the peat as if they 
had terminated two branches resulting from a dichotomy. Hemispherical pro- 
jections and adventitious branches are not known to occur in this species. The 
most satisfactory specimens of rhizomes in situ (Part I, fig. 13) show that they grew 
horizontally and were cylindrical, stem-like, and dichotomously branched. They 
bore rhizoids on the lower surface, sometimes on large bulges. The features thus 
briefly touched upon will be found expressed in the reconstruction. 
We have little to add to the description of this species, but the opportunity may 
be taken to figure an obliquely longitudinal section of the apical region of a branch 
(PI. IV, figs. 17 and 18). The actual apical meristem is contracted and collapsed, 
but the progressive enlargement and elongation of the cells behind this can be traced. 
The fact that the layer ofi cells with dark contents just below the outer cortex can 
be traced near to, but not up to, the apex is of interest (fig. 17). 
As pointed out above, hemispherical projections like those of Rliynia Gwynne- 
Vaughani have not been found in R. major. Further, while the stems of the latter 
plant may be very perfectly preserved or badly decayed, they do not so commonly 
exhibit the wound-reactions around cavities due to necrosis described for R. Givynne- 
Vaugliani. Examples of necrosed areas and of wound-reactions that must have 
taken place during life have, however, been met with. This is shown in a very 
striking fashion by the two stems represented in fig. 19 on PI. IV. In the case of 
the stem on the left, the cortical tissue had disappeared from a sector of the stem as 
seen in transverse section. Regenerative activity involving enlargement and division 
of the cells thus exposed had taken place. This proceeded both from cells of the 
cortex and of the phloem (fig. 20). In the other stem there was no cavity, but the 
region of cortex below and around a dark necrosed patch had been the seat of 
enlargement and division of cells. It contrasts with the normal cortex in the 
arrangement of the groups of newly formed cells and the whole character of the 
tissue. A portion of the disturbed growth in the neighbourhood of the stele of this 
stem is shown more highly magnified in fig. 21. 
The enlargement of the cells that here precedes their division can be compared 
with another appearance, represented in fig. 22 for R. major. In the case of this 
