FILICES. 169 



to the development of a covering of adventitious roots, which is of almost 

 universal occurrence. It is this thick felt of roots more than anything else 

 which conceals from our view the surface of the stem and the form of the 

 trace in the leaf-scars. There are no silicified specimens without this cover- 

 ing, if we except Caulopteris Giffordi, Lesq. 1 from the Coal-measures of 

 Illinois which belongs here, and only a few instances can be adduced among 

 the stems that are preserved as casts, and these perhaps represent the upper- 

 most portions of the stem. Here too the leaf-scars are indifferently pre- 

 served as regards matters of detail, though it appears that the relative 

 positions of the leaves were not always the same ; in Psaronius Freislebeni 2 , 

 for example, the leaves are in spirals with six orthostichies, while P. arena- 

 ecus 3 shows only four orthostichies and P. carbonifer (P. musaeformis, 

 Corda 4 ) has its leaves in two lines after the manner of Zippea and Mega- 

 phytum. That there are the like differences also in the stems which are 

 surrounded with a covering of roots may be concluded from the distribution 

 of the vascular bundles, which goes hand in hand with the position of the 

 leaves. 



The anatomy of the stems of Psaroniae is very well known, thanks to 

 Stenzel's 5 careful and comprehensive researches founded chiefly on materials 

 from Saxony and Bohemia. The French specimens and those which are 

 not European have not yet been sufficiently studied. In the parenchyma, 

 which has in very many cases been destroyed, we find the characteristic 

 concentric net-work of vascular bundles, the several circles of which, appear 

 to be united together here and there by radial connecting strands. The 

 transverse sections of the vascular bundles form broad curved plates which 

 in many cases have their margins bent inwards till they become hooked, 

 and are developed in larger or smaller numbers and are quite loosely or 

 extremely closely packed, according to the species. An instance of loose 

 arrangement of the bundles is seen in Psaronius Bibractensis c , in which 

 moreover, in contrast to all other known species, solid sclerenchyma-bands 

 of the same shape as the vascular plates are seen lying between them. The 

 opposite condition appears in P. infarctus, Ung. 7 , in which the plates almost 

 touch one another. A firm lignified sheath enclosing the whole bundle- 

 system of the stem is often present, but may be wanting both in this and in 

 other species. The relative position of the vascular bundles on the trans- 

 verse section of the stem is different in different species, and this is in direct 

 connection with the phyllotaxy, as we learn from the specimens described 

 above, which are preserved in the form of casts and show the outer surface. 

 In the specimens which have the leaves arranged in two lines (Fig. 16) they 



1 Lesquereux (1), p. 343, t. 60, ff. I, 2. 2 Corda (1), t. 29. 3 Corda (1), t. 28, ff. 5-9. 



4 Corda (1), t. 45, f. 3. ' Stenzel (1) ; Goppert (3> * Renault (2,, t. 26, f. 2. 7 Gopperl 



(3), t. 5, f. i. 



