618 DR R. KIDSTON AND PROF. W. H. LANG ON OLD RED SANDSTONE PLANTS 
was a well-developed system of small intercellular spaces. The peculiar hemi- 
spherical projections of Rliynia Gwynne-Vaughani were the seat of adventitious 
lateral branches, and, whatever their other functions, may provisionally be 
regarded as dormant branches. The sporangia correspond to transformed and 
more or less specialised ends of stems of various sizes. Their thick wall was 
indehiscent, and the epidermis was usually specially thickened. There was a 
peculiar (and possibly tracheidal) tapetum. The spores were developed in 
tetrads and had cuticularised walls. No sterile cells were mixed with the 
spores. In Hornea the central tissue formed a sterile columella projecting into 
the sporangial cavity. 
This is a simpler type of plant than is known in any existing Vascular Cryptogam, 
or in any extinct forms from the Carboniferous period onwards. In the Devonian 
period, however, there are indications of plants of correspondingly simple 
morphology. It will be sufficient to mention here Sporogonites as possibly 
related to the Rhyniacese. 
Sporogonites exuberans, Halle,* from the Lower Devonian rocks of Roragen, 
Norway, consists of a long unbranched axis terminating in a sporogonial or sporangial 
structure which is similar to the sporangium of Hornea in a number of characters. 
There are distinct differences, however, but the two agree in the presence of a 
columella rendering the spore-containing cavity dome-shaped. Halle regards 
Sporogonites as a sporogonium and as finding its “ nearest analogy in the sporogonia 
of the Bryophyta.”t Our fuller knowledge of Hornea , however, lends weight to 
another suggestion of Halle that “ the possibility must be faced that it may 
represent only the upper part of a more highly developed sporophyte, perhaps on 
the line of descent of the pteridophytes.” J So far as the evidence afforded by the 
remains of Sporogonites goes, it does not establish the bryophytic nature of the 
plant. In showing a general resemblance to sporogonia of Bryophytes the sporangia 
of Hornea and Rliynia agree with Sporogonites , and in them the relations of the 
sporangia to the whole simple vascular plant is known. 
While the comparisons with Sporogonites and with some undescribed im- 
pressions which we have seen are of great interest, our fairly complete knowledge 
of the structure as well as the external morphology of Rliynia and Hornea makes 
them more suitable for comparison with other plants. In dealing with such 
simply organised Pteridophyta comparisons must be widely extended, but at present 
are best only indicated in outline. 
The simple organisation of the sporophytes of Rliynia and Hornea may there- 
fore be briefly compared with some other Pteridophyta, with Bryophyta, and 
with Algae. 
* Halle, T. G., “ Lower Devonian Plants from Roragen in Norway,” Kongl. Svensk. Vetenskapsaked. Handlingar, 
Bd. 57, 1916, p. 27, pi. iii, figs. 10-32. 
t Loc. tit., p. 31. 
| Loc. tit., p. 40. 
