466 W. Carruthers — Tree-ferns of the Coal-measures. 



are very closely allied to a group of Fern steins which I have already 

 placed together under the name of Chelepteris. The stem structure 

 of the common Tree-fern is represented by the genus Caulojpteris, of 

 which I have six species of Carboniferous age. 



The third and extinct group is represented by Corda's genus Stem- 

 matopteris, only now known to be British, and by Psaroniiis, which 

 is, however, not a separate generic form ; it is based on the internal 

 structure of the stems of which Corda's genus is the external aspect. 

 The chief characters of Psaronius have been drawn from the struc- 

 ture of the aerial roots which invest the stem, from which indeed 

 the generic designation was derived ; while the structure of the stem 

 itself has been overlooked. But this is really of the first import- 

 ance, as will appear from the following description which I have 

 been able to make from a finely-preserved specimen of an un- 

 described species in the British Museum, and from the figures of 

 Cotta and Corda. The circumference of the stem was composed of 

 a continuous envelope of indurated tissue ; within this there were 

 perpendicular tracts of vascular tissue never penetrated by any mesh. 

 Between these tracts the leaves were given off in perpendicular 

 series, the large single leaf bundles coming right out from the central 

 parenchyma, where they existed as well-formed bundles, filling up 

 more or less completely the medullary cavity. In one form {Zippea) 

 the leaves are opposite, and the great proportion of the circumference 

 of the stem is made up of the persistent and common vascular tissue : 

 in others (species of Psaronius) the permanent elements of the stem 

 consist of three, four, six, or more perpendicular tracts. 



The first two groups are analogous in the arrangement of the parts 

 of their stems to that which exists in the first year's growth of a 

 dicotyledon. In both there is a parenchymatous medulla surrounded 

 by a continuous vascular cylinder, which is perforated in regular 

 manner by meshes for the passage out of the vascular elements of 

 the appendages. The stems of the third group have a structure 

 analogous to that which is found in the stems of monocotyledons, for 

 in both we have the vascular bundles of the appendages existing in 

 the parenchymatous axis, and passing out independently of any 

 closed cylinder. The permanent elements of the circumference of 

 the stems of Psaronius, are, however, without any analogue in the 

 monocotyledonous stems. 



There seems then good reason for establishing two groups of Ferns, 

 with differences characteristic of their stems, comparable to those 

 which distinguish the stems of monocotyledons from those of dico- 

 tyledons. But the caution I have always insisted on in dealing only 

 with vegetative organs is specially required here, for I have dis- 

 covered, I believe, the fruiting fronds of one species of this group of 

 plants. With the Bath specimens of Stemmatopteris insignis, Corda, 

 as well as with those found on the Continent, the fronds oi' Pecopteris 

 arhorescens are always associated. It is the only Fern found with 

 some of the Bath specimens. It is also to be observed that the bases 

 of the stipes correspond with the size of the leaf-scai'S on the stems. 

 These facts are not absolutely sufficient for the correlation of the 



