390 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
mutual pressure. The wall, as preserved, is usually one cell thick and 
is provided with a conspicuous annulus, extending partly round the 
sporangium, and, when cut lengthways, strongly recalling the fa- 
miliar Polypodiaceous annulus. (Fig. 7.) Transverse sections, how- 
ever, show that the annulus is really two cells in width. The spores, 
often well preserved, are numerous, and of one kind only, so far as 
observed. No clear case of a uniseriate annulus in Fern sporangia 
of Paleozoic age has yet been demonstrated. 
The fortunate discovery of the germination of spores, with the 
development of a prothallus and rhizoids within the sporangium 
of Stauropteris Oldhamia, is good evidence that the latter, at any 
rate, was a true Fern. Another similar though larger sporangium 
containing germinating spores is probably also referable to Staurop- 
teris. 
The probability is in favor of an affinity between the genus Stau- 
ropteris and the Botryopteridex, though the sporangial characters 
scarcely admit of a definite reference to that family. The discovery 
of the germinating spores just mentioned much strengthens the con- 
clusion that the Botryopteridee and allied Paleozoic plants were 
really members of an ancient race of Ferns. 
PALEOZOIC MARATTIACEA, 
No conclusion in Paleobotany has met with more general accept- 
ance than that of the prevalence of Marattiaceous Ferns in the Car- 
boniferous Flora. The evidence is well known, and needs only the 
briefest recapitulation here. A number of fructifications, such as 
Ptychocarpus, Scolecopteris, Asterotheca, Hawlea, etc. (see fig. 8), 
agreeing closely with the synangia of recent Marattiacez, have been 
found in situ on fronds of the Pecopteris type. In some cases the 
minute structure of the fructifications can be studied in petrified 
specimens, and entirely confirms the inference drawn from external 
characters. It would be difficult, in fact, to find clearer evidence of 
affinity between a recent and a fossil group of plants than is afforded 
by these synangia. But this is not all. A number of petrified stems, 
constituting the genus Psaronius, are known, in which the anatomy 
has been fully investigated, and proves to agree more nearly with the 
structure of Marattiacez than with that of any other group of plants. 
The anatomical agreement holds gocJ in spite of a considerable dif- 
ference in habit, the fossil stems (known as Caulopteris, Megaphy- 
ton, etc., when preserved as casts) having attained arboreal stature. 
Recent investigation by Rudolf, of the structure of the Psaronii, 
with special reference to their relation to Marattiaceee, further con- 
firms their affinity. From the evidence of comparative structure and 
association it appears certain that the Psaronius stems bore the foli- 
age of Pecopteris, of the same nature as the leaves on which the 
