Reports & Proceedings — Edinburgh Geological Society. 187 



The plant bore large cylindrical sporangia with thick walls, and 

 contained numerous spores of one kind developed in tetrads. 



Rhynia Gwynne-Vaughani was also rootless and leafless, and very 

 similar in morphology and anatomy to R. major, but was a smaller 

 species, jorobably not more than 20 cm. in height. It differed from 

 R. major in having small hemispherical protuberances derived from 

 the suj)erficial tissues of the stem. These might remain as small 

 protuberances, or develop rhizoids. Sometimes in place of the 

 jjrotuberances adventitious branches were produced, or bulbil-like 

 growths attached by a narrow base that probably served for 

 vegetative reproduction. The sporangia were of similar structure 

 to those of R. major, but much smaller, and contained numerous 

 spores of one kind. 



Hornea Lignieri was a small rootless and leafless plant, whose 

 stems branched dichotomously, and attained a diameter of 2 mm. 

 They arose from a branched rhizome which had no vascular strand 

 of its own. The stele of the stem consisted of a central cylinder of 

 xylem, with smaller central and larger peripheral tracheides 

 surrounded by a zone of phloem. The thickening on the tracheide 

 walls is in the form of irregularly connected rings or a spiral. The 

 stem has a well-defined cuticle and epidermis, but the cortical 

 tissues are not clearly distinguishable into inner and outer zones. 

 The cortex is usually very imperfectly preserved. 



The sporangial cavity of the indehiscent sporangium is enclosed 

 by a fairly thick wall, azid had a sterile column of tissue or columella 

 projecting so far from the base that the actual spore cavity is dome- 

 shaped. The sporangia arose by the transformation of the tips of 

 certain branches. The numerous spores are of one kind. 



Asteroxylon Mackiei was a larger and more complex plant than 

 any of the others. The stems arose from rhizomes without absorbent 

 hairs. They attained a diameter of 5 mm. Some of the rhizome 

 branches bent upwards and developed into leafy stems. The 

 rhizomes have an epidermis with outer and inner cortex, and a 

 cylindrical strand of xylem surrounded by a zone of phloem. The 

 transition area between the rhizome and stem bears stomata and 

 scale-leaves, and the xylem gradually assumes the stellate form of 

 the stem xylem. The stem has a cuticle, epidermis with stomata, 

 outer and inner cortex — the latter usually being separable into three 

 zones — an outer, middle trabecular, and inner zone. The stele 

 consists of a stellate strand of xylem enclosed in a zone of a phloem. 

 The tracheides of both rhizome and stem have a prominent 

 spiral thickening. The stem bears numerous simple leaves about 

 5 mm. long without any vascular bundle in the free portion, the 

 leaf-trace stopping at the enlarged leaf-base. The free portion of 

 the leaf is oval in transverse section. 



The probable fertile region consisted of slender branched leafless 

 axes and pearshaped sporangia about 1 mm. long, with regular 

 apical dehiscence. Homosporous. Spores developed into tetrads. 



