SHOWING STRUCTURE, FROM THE RHYNIE CHERT BED, ABERDEENSHIRE. 611 
Rhynia major. 
Plant larger in all its parts than R. Gwynne-Vaughani. Aerial stems tapering 
upwards, and ranging in thickness from 6 mm. to 1'5 mm. or less. No hemispherical 
projections or adventitious lateral branches. Stele large, xylem strand of numerous 
tracheides differentiated as smaller central and larger peripheral tracheides. 
Sporangia reaching a length of 12 mm. and a diameter of 4 mm. Sporangial wall 
about *3-'4 mm. thick. Spores about 65 g in diameter. 
Locality. — Muir of Rhynie, Aberdeenshire. 
Horizon. — Old Red Sandstone (not younger than the Middle Division of the Old 
Red Sandstone of Scotland). 
Hornea Lignieri, n.sp. (Plates IY-X.) 
Another vascular plant from the Rhynie peat-bed agreed in general build with 
Rhynia, but differed in the sporangia having a columella of sterile tissue, around and 
above which the dome-shaped spore-sac extends. We regard it as a distinct, though 
allied, genus, and have named it after Dr Horne, to whose energy and interest the 
successful discovery of the Rhynie peat-bed in situ is largely due. The specific name 
has been given in reference to the acute morphological speculations of the late 
Professor Lignier, some of which gain confirmation and reality from the discovery 
of these simple types of Vascular Cryptogams. 
The remains of Hornea occur in considerable quantity, at places forming an 
almost pure peat and elsewhere mixed with the other plants of the Rhynie deposit. 
The preservation is not quite so good as in the case of Rhynia and Asteroxylon, but 
shows all the essential structural features. 
Hornea Lignieri resembled Rhynia in being a rootless and leafless plant, 
differentiated into rhizome, dichotomously branched cylindrical stems, and terminal 
sporangia. The continuity of these parts has been established. From the lobed 
tuberous rhizome, which was probably subterranean but might have been only partly 
embedded in the soil, a number of cylindrical stems arose separately. These bore no 
appendages, nor did they have hemispherical projections or lateral branches. They 
were from about 2 mm. to slightly under 1 mm. in diameter, and branched dichoto- 
mously. This occurs in the larger stems, but was probably more frequently repeated 
in the upper region of the plant, the stems diminishing in thickness as they 
subdivided. The sporangia terminated stems of various diameters, and show a 
corresponding range in size. The transformation of the end of a stem into a 
sporangium often affected a nascent dichotomy, the branching being then evident 
in the construction of the columellate sporangium. 
The rhizome, stems, and sporangia may now be described in detail. 
TRANS. ROY. SOC. EDIN., VOL. LII, PART III (NO. 24). 
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