1920-21.] On the Old Red Sandstone Plants. 
117 
XII. — On the Old Red Sandstone Plants showing Structure, from 
the Rhynie Ohert Bed, Aberdeenshire. Part IV. Restora- 
tions of the Vascular Cryptogams, and discussion of their 
bearing on the General Morphology of the Pteridophyta and 
the Origin of the Organisation of Land-Plants. Part V. The 
Thallophyta occurring in the Peat Bed; the Succession of 
the Plants throughout a Vertical Section of the Bed, and 
the Conditions of Accumulation and Preservation of the 
Deposit. By Dr R. Kidston, LL.D., D.Sc., F.R.S., and Professor 
W. H. Lang, D.Sc., F.R.S. 
(Read May 2, 1921. MS. of Part IV received May 2, 1921, and Part V June 28, 1921.) 
(Abstract. Papers published in full in Transactions , VoL LII.) 
Part IV. — This paper concludes the authors’ account of the Vascular 
Cryptogams found in the Rhynie deposit. Restorations of the four plants, 
Rhynia Gwynne-Vaughani, R. major , Hornea Lignieri, and Asteroxylon 
Mackiei, are given. A few additional features, supplementary to the 
descriptions of these plants in the preceding papers of the series, are 
described and illustrated. The hemispherical projections of Rhynia 
Gwynne-Vaughani are shown to have originated underneath stomata. 
A comparison is made between them and certain intumescences in existing 
plants. Areas of necrosis and marked wound-reactions of the tissues 
around them are described for both species of Rhynia. The apex of a 
stem of R. major is figured. For Asteroxylon additional figures are given 
of a large rhizome, of the leaf-arrangement and immature structure of the 
stem in the region of a shoot-apex, and of the longitudinal markings on 
the epidermal cells resembling those found in Rhynia Gwynne-Vaughani. 
The discussion summarises the authors’ views on the main bearings of the 
facts described in Parts 1-4 on various problems in plant morphology. 
Part V. — The Thallophyta occurring in the peat bed ; the succession of 
the plants throughout a vertical section of the bed, and the conditions of 
accumulation and preservation of the deposit. 
In this concluding part of this series of papers the Thallophyta found 
in the silicified peat are described. The most abundant are Fungi, repre- 
sented by hyphse of the mycelium and vesicles or resting-spores borne on 
this. With the exception of one specimen, the hyphse were non-septate and 
