ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 195 



Pteridopbytes obtained from the silicified peat-bed at Rhynie in Aber- 

 deenshire. Rhynia major represents a new species, and Hornea Linnieri 

 a new genus and species. Rhynia w-as a gregarious, rootless and leaf- 

 less plant growing erect from a subterranean irhizorae and branched 

 dichotomously. It bore stomata ; and its stele consisted of a zone of 

 phloem surrounding a strand of tracheides. The sporangia were 

 cylindrical, without columella, and were terminal on aerial stems. The 

 spores were of one sort only, were developed in tetrads, and had a 

 cuticularized wall. Hornea was also rootless and leafless, its dicho- 

 tomous aerial stems growing up from protocorm-like rhizomes. The 

 sporangia were terminal on ultimate branches, having a basal columella 

 projecting up into the sporangial cavity, and the cuticularized spores 

 were developed in tetrads. The family Rhyniacea3 is placed in a 

 special class, Psilophy tales. The Rhyniacese were land plants, and may 

 afford some clue to the origin of the land-growing sporophyte, as 

 suggesting derivation from an algal ancestry comparable in habit with 

 FarceVariafadiyiaia. A. <tepp. 



Old Red Sandstone Plants from the Rhynie Chert. Part III. : 

 Asteroxylon Mackiei. — R. Kidston and W. H. Lang {Trans. Roy. 

 Soc. Edmhuryh, 11)20, 52, 643-80, 17 plates). An account of the 

 structure of Asteroxylon, well-preserved fragments of which were found 

 with the remarkable plants Rhynia and Hornea in the silicified peat- 

 bed at Rhynie, which belongs to the geological horizon of the Old Red 

 Sandstone. All these genera are referred to the Psilophytales, a class 

 of the Pteridophyta ; and while Rhynia and Hornea constitute the 

 family Rhyniacefe, Asteroxylon (characterized by the stellate outline of 

 its cauline xylem in transverse section) represents a separate fumily. 

 Asteroxylon had a leafless rhizome, from which arose branched aerial 

 stems bearing numerous small leaves. The stele (xylem) of the 

 rhizome was cylindric, but in the stem was stellate and gave off leaf- 

 traces. The fertile region appears to have consisted of slender branched 

 leafless axes bearing pyriform sporangia of moderate size, with definite 

 dehiscence at the wider free encl. The tracheides of the metaxylem and 

 protoxylem have a peculiar type of spiral thickening. A. G. 



Morphology of the Stele of Platyzoma microphyllum.— John 

 McLean Thompson (Trans. Roy. Soc. Edinhuryh, 1920, 52. ,571-'.)5, 

 3 pis. and figs.). A discussion of the stelar problem of Platyzoma, 

 with a resume of the facts of stelar structure previously recorded for 

 the plant and of the theories founded upon them by Poirault, Jeffrey, 

 Boodle and Tansley. The author is unsatisfied as to the nature and origin 

 of the medullated stele, and describes the structure of a number of 

 recently acquired specimens, which levealed neither a soleiiostelic 

 condition nor evidence of degenerate stelar gaps or of inner phloem. 

 One small specimen showed interesting features which are illustrated in 

 detail. In this (examined from- the broken base upwards) the pith and 

 inner endodermis became narrowed to a vanishing point, and a 

 medullated protostele was locally established ; the pith then again 

 expanded and within it there arose de ?iovo an inner endodermis at first 

 irregular, then definitely tubular to the apex of the stem. L'pon the 



