[Illustration: FIG. 295. _Psaronius_ stem with roots. (Much reduced. After Grand’Eury.)] The researches of Grand’Eury[1061] led to the discovery that certain Psaronius stems bore fronds of the _Pecopteris_ type some of which bore sori of the _Asterotheca_ or _Scolecopteris_ type. The same author[1062] has also contributed many interesting facts, obtained by an examination of the relation of Psaronius stems to the sediments of French Coal-fields in which they occur, in regard to habitat and manner of growth. The specimen represented in fig. 295 shows a portion of a Psaronius stem, the upper part of which illustrates the Caulopteris state of preservation, while the lower part is covered by a mass of roots. It is probable, as Rudolph[1063] suggests, that this rich development of roots, which gives to an old Psaronius stem the appearance of an elongated cone, may have served an important mechanical purpose analogous to the secondary thickening in a Dicotyledon or a Conifer. A specimen of _Psaronius Cottai_ in the Hofmuseum, Vienna, is cited in illustration of the enormous breadth of the root-system: the radii of the stem proper and of the encasing cylinder of roots bear the ratio 17 to 165. The comparatively frequent occurrence of a lacunar cortex in the roots points to the growth of the stems in swampy ground, a conclusion in harmony with the evidence afforded by the anatomical features of many other Palaeozoic genera. • • • • • _Psaronius_ may be briefly defined as follows:—