SHOWING STRUCTURE, FROM THE RHYNIE CHERT BED, ABERDEENSHIRE. 671 
Devonian rocks. Some specimens in which sporangia are terminal on ultimate 
ramifications are of special interest, and have been compared by other inves- 
tigators to Psilophyton. These include Dimeripteris * and Rhacophyton con- 
drusorum t from the Upper Devonian. Perhaps the most striking comparison on 
these lines, however, is with the better, but still imperfectly, known plant Stauro- 
pteris from the Carboniferous rocks, especially if, as suggested by Lignier,| it should 
prove to have grown as an independent “ frond,” and not have been borne on a stem. 
. On reviewing the main comparisons, which we have been led to make or suggest 
with Asteroxylon , it will be seen that the only plants with which there may be 
agreement in total organisation are Psilophyton and some other more or less 
incompletely known archaic vascular plants. A definite conclusion cannot be reached 
on this question, owing to the uncertainty as to essential facts, both for Asteroxylon 
and all these other ancient plants. 
The comparisons with the Psilotales as regards both general organisation and 
anatomy are close and striking. This group may be regarded as representing in 
a modified and specialised form the features of the Asteroxylon type of plant as 
persisting to the present time. The Psilotales must, however, be maintained as a 
distinct class of Pteridophyta. 
The comparison with the Lycopodiales, and especially with Lycopodium, comes 
out clearly in the general habit, and particularly in the anatomy, though comparison 
cannot at present be extended to the reproductive organs. The antiquity of the 
general type of construction of the shoot and stele exhibited by Lycopodium is 
clearly established by our knowledge of Asteroxylon. 
The characters of Asteroxylon suggest an advance from a more primitive type in 
the direction of the Lycopodiales rather than of the Filicales. There are, however, 
some interesting resemblances to archaic Ferns or plants which can be regarded 
as on the line to the Filicales. 
The possible fertile region of Asteroxylon, though imperfectly known, appears 
to allow of comparison both with primitive Filicales and with the sporangiophoric 
Pteridophyta. This suggests a general point of view from which all sporangiophores 
may be regarded. 
The Characters and Systematic Position of Asteroxylon considered in Relation 
to Lignier’s Views as to the Evolution of Pteridophyta, and Halle’s 
Application of them to the Devonian Floras. 
The characters of Asteroxylon and the comparisons with other Pteridophyta 
suggested above are consistent with a general view of the sporophyte in land-plants 
'• ScHMALHAUSBN, J., “Ueber devonische Pflanzen aus dem Donetz-Becken,” Mem. du Comite Ge'ol., vol. viii, 
No. 3, p. 29, 1894. 
f Crispin, F., “ Description de quelqu'es plantes fossiles de l’etage des Psammites du Condroz (Devonien 
Superieur),” Bull, de V Acad. roy. de Belgique, vol. xxxviii, p. 1, 1874. ( Psilophyton condrusorum.) Crispin, F., 
“ Observations sur quelques plantes fossiles de depots devonien, etc.,” Bull. Soc. roy. de Botan. de Belgique, vol. xiv, 
p. 224, 1875. (Footnote, Rhacophyton condrusorum.) t Loc. cit., 1912. 
