3 i2 STUDIES IN FOSSIL BOTANY 



side of the leaf-trace, between the latter and the stele 

 of the stem, is of special interest. It is continuous with 

 the adaxial part of the original leaf-trace, and as it 

 separates, assumes an elliptical form in transverse 

 section (see Fig. 115, ax), with the long axis placed 

 tangentially. It consists of a ring of xylem, with 

 large tracheides, surrounded by a zone of phloem, and 

 at the centre is a group of small tracheides accompanied 

 by parenchyma. In fact, the structure of this bundle 

 is that of the stele of the main stem, in an extremely 

 simplified form. The axillary strand, as it is best 

 termed, passed out into a cylindrical appendage, placed 

 exactly in the axil between stem and leaf, and hence 

 appropriately named by Stenzel the axillary shoot (Fig. 

 115, ax). This curious organ occurs in three out of the 

 four forms of Zygopteris in which the stem is known, 1 

 but has not, so far as I am aware, been found in 

 any other genus of fossil Ferns. There is, however, 

 the closest possible analogy with the axillary branches 

 of the recent Hymenophyllaceae, a family with which, 

 in various other respects also, the Botryopterideae have 

 much in common. Stenzel, the discoverer of the 

 axillary shoots of Zygopteris, at first suggested another 

 possible view of their nature, namely, that they might 

 represent the fertile ventral lobe of the leaf, as in the 

 Ophioglosseae. This was, at the time, a sufficiently 

 probable interpretation, but was subsequently withdrawn 

 by the author, on the ground that transitional forms 

 occur, which are intermediate in structure between the 



1 The bundle marked r in Renault's figure (Flore fossih d Autun et 

 cPEpinac, Part ii. Plate xxxi. Fig. 2) of Z. Brongniarti, from its form and 

 position, manifestly belongs, as Stenzel detected, to "the axillary shoot, 

 though interpreted by the author as an adventitious root. 



