SHOWING STRUCTURE, FROM THE RHYNIE CHERT BED, ARERDEENSHIRE. 669 
that larger and smaller stems of Asteroxylon, leafless branches of simpler structure, 
and the peculiar axes and sporangia can be distinguished in this portion of the 
Rhynie peat (PI. XV). The comparison is with the larger and smaller branches, 
the finer ultimate subdivisions, and the sporangia of Stauropteris. The reader may 
compare fig. 104 of this paper with fig. 321 of vol. ii of Seward’s Fossil Plants, or 
with fig. 1 on pi. i of Bertrand’s memoir on the Zygopteridese. 
( b ) No close comparisons can be made with certainty between the small axes 
with peculiar structure and other plants. The general resemblances they present, 
however, to ultimate fertile ramifications of Stauropteris on the one hand, and on the 
other to the sporangiophores of various extinct and existing Pteridophyta, may be 
indicated. We are inclined to attach considerable significance to this. 
(c) The sporangia, with their thick wall, specially thickened epidermal layer 
without definite annulus, and terminal dehiscence, can be compared most closely 
with those of Stauropteris. Less close, but interesting, comparisons may be made 
with the sporangia of the Ophioglossacese, especially Helminthostachys, of the 
Psilotacese, and of Lycopodium and Selaginella. 
5. Owing to the absence of conclusive evidence that the small axes with peculiar 
structure are the ultimate fertile branches of Asteroxylon and bore the associated 
sporangia, we enter a more speculative region in seeking for comparisons with 
the whole plant of Asteroxylon as completed by combining these as its reproductive 
organs. 
If this assumption proves to be correct, the general habit and morphology of 
Asteroxylon would be comparable with that of some Early Devonian plants, the best 
known of which is Psilophyton princeps. 
The plant of Psilophyton princeps, as reconstructed by Dawson in his well-known 
figure,* had horizontal rhizomes bearing more slender root-like appendages, erect 
branched aerial stems with small spine-like leaves, and large sporangia borne ter- 
minally on the smooth ultimate branches. The known specimens of the plant do not 
suffice to establish this reconstruction. There is doubt as to the appearance of 
the rhizome. The characters of the aerial stems, with their spiny leaves and dicho- 
tomous or lateral branching, are confirmed by specimens known from a number of 
localities. The actual connection of the smooth branched axes bearing the large 
sporangia with the leafy shoots is not established. They have, however, been found in 
association with the stems of Psilophyton in Norway and France as well as in the 
original locality at Gaspe in Canada, a circumstance that cannot be ignored. Halle f 
has separated the stalked sporangia under the name Dawsonites arcuatus, on the 
ground of absence of proof of connection with Psilophyton. He, however, recognises 
in Psilophyton Goldschmidti a plant showing that smooth branch systems are borne 
* Geological History of Plants, fig. 19. 
t Haxltc, T. G., “Lower Devonian Plants from Roragen in Norway,” Kungl. Svenska Vetenskapsakademiens 
Handlingcvr, Bd. 57 (1916), p. 1, 
