KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 57. N:0 I. 15 



mination of some of Dawson's specimens. The following discussion will be found to 

 agree closely with the opinions already expressed by White, althougli it is merely the 

 result of a review of Dawson's papers and treats the matter in a somewhat different 

 manner. 



In his first description of Psilophyton princeps, Dawson gives the following dia- 

 gnoser »Lycopodiaceous plants, branching dichotomously, and covered with interrupted 

 ridges or closely appressed minute leaves; the stems springing from a rhizoma having 

 circular areoles, sending forth cylindrical rootlets. Internal structure: an axis of scalari- 

 form vessels, surrounded by a cylinder of parenchymatous cells, and by an outer cortical 

 cylinder of elongated woody cells (prosenchyma). Fructification probably in lateral 

 masses, protected by leafy bracts. » 



As will appear from this diagnose, Dawson already in his first description of the 

 species refers to it remains of very different nature on the supposition that they represent 

 different parts of the same kind of plant. The well-known restored figure of Psilophyton 

 princeps published in this first description shows a creeping rhizome, from the ventral 

 side of which spring short vertical rootlets, whereas the upper side gives rise to upright 

 bifurcating aerial shoots. With the exception of this restored figure, Dawson does not 

 give any illustration of the connection between the rhizomes and the aerial stems. The 

 only specimen of the rhizome figured in this place (fig. la) is very poor, and differs 

 from those of the aerial stems only in size and through the occurrence of circular areoles 

 supposed to represent root-scars. Similar rounded areoles occur, however, also in aerial 

 stems figured by Dawson on a låter occasion (Dawson 1871, pl. 9, figs. 99, 104, 110) and 

 are in that case regarded as scars of the spines or leaves. The bifurcating aerial shoots 

 are characterized by the circinate nature of the young branch-tops and by the occurrence 

 of elongated ridge-like markings or »closely appressed minute leaves». These leaf- or 

 spine-bearing aerial stems are the best characterized of all the plant-remains figured by 

 Dawson in this first publication as belonging to Psilophyton princeps. The figures given 

 of these specimens in the paper mentioned are very unsatisfactory, however, and convey 

 no clear idea of their nature. 



In addition to the impressions of stems and branches Dawson describes in the 

 same place (p. 480, fig. 1, k-n) fragments of stems with the structure preserved. No 

 proof is offered of their relation to the impressions of »leaf-bearing » branches. Solms 

 Laubach (1895), in his critical review of the literature on Psilophyton, remarks on this 

 fact and treats the petrified specimens separately from the spine-bearing branches. In 

 a låter paper (1863, p. 465; pl. 18, fig. 22) Dawson describes and figures another speci- 

 men in which the anatomical structure is preserved and which is stated to present similar 

 surface markings as the impressions. Dawson's observations on the internal structure 

 of Psilophyton princeps will be further considered in the following pages. 



As the fructification of Psilophyton princeps, Dawson figures in his first paper a 

 very obscure object (fig. le), consisting of a branch supposed to carry a curious lobed 

 structure. This latter, however, as remarked by Solms-Laubach (1895, p. 71), cer- 

 tainly does not belong to the branch but is merely adpressed to it. The specimen is 

 of no value whatever and need not be further considered. 



