STEUCTURE OF LEPIDOSTROBUS. 363 



the primary cortex into three more or less distinct zones, of which the middle zone was 

 of a softer and often of a very spongy or even of a trabecular character. The same is 

 true also of Lepidostrobus, in which only the primary tissues are developed. 



Beyond the inner space (PL XXXVI. fig. 2, i.s.), the inner cortex, i.e., is well shown, it 

 is thin (narrow radially), varying from 2-6 rows of cells in radial thickness, the maximimi 

 given here being about equal to that of L. oldhamius ((3) (see PI. XXXVII. fig. 23, i.e.). 

 In vertical section (PL XXXVI. fig. 5, i.e.) the cells are seen to be somewhat elongated 

 in the vertical direction and to have, generally, oblique cross-walls. The cells are also 

 seen to be larger than those of the tissue immediately investing the axis. The transverse 

 section (PL XXXVI. fig. 2) shows the way in which the leaf-trace bundles pass through the 

 inner cortex, and how they obtain from it a sheath which, as we shall see, accompanies 

 them into the sporophylls. 



Outside the inner cortex is the wide space (PL XXXVI. fig. 1, m.c, and fig. 2, tn.c.) 

 representing the middle cortex. No trace of the tissue formerly occupying this space can 

 be seen in any of the sections, either at its inner or outer limit or around the leaf-trace 

 bundles by which it is traversed, a fact to be explained only on the assumption that the 

 tissue was of an exceedingly delicate nature. 



The outer cortex is well preserved and has a thickness (between the points of insertion 

 of the sporophylls) of about 5 millim. The cells are thick-walled, and many show the 

 peculiar structure represented in tangential section on PL XXXVII. fig. 15, o.c. ; in radial 

 section on PL XXXVI. fig. 7, o.c, and fig. 8 ; and in transverse section on PL XXXVI. 

 fig. 9. As already pointed out, these cells are tliick-walled, and they show in their interior 

 what appears to be a shrunken lenticular mass probably representing the remains of some 

 peculiar contents, or possihly only a swollen inner layer of the cell-wall. 



These peculiar cells appear to be highly characteristic of this form of Lepidostrobus, 

 and can be seen not only in the outer cortex of the axis, but also in the cells which form 

 the cortex of the sporophylls (see PL XXXVI. fig. 7). Sections of the latter, even when 

 forming the free scales (laminae) at the periphery of the cone, still exhibit a peripheral zone 

 of cells possessing much the same structure (PL XXXVII. fig. 17). Cells of tliis character, 

 though highly characteristic of the form under consideration, are still not confined to it ; 

 some cells presenting similar characters can be seen in sections of other forms. In the 

 longitudinal section of Wild's Cone (L. oldhamius ((B), C.N. 1776 a, see PL XXXVIII. 

 fig. 26, showing the cells of the outer cortex in longitudinal section), in which the 

 structure of the outer cortex is perfectly preserved, no trace of such cells can be seen, 

 though similar cells can be seen around the periphery of the sporophylls in the same 

 section. Moreover, in L. oldhamius (a) the outer cortical cells are on an average 

 much rounder and shorter than those of Z. oldhamius (/3), (ep. PL XXXVI. fig. 8 and 

 PL XXX VI II. fig. 26), making it almost certain that the differences are not merely due 

 to peculiarities in mineralization. 



The Leaf -trace Bundles. — The leaf -trace bundles arise, as is usual in the Lepidodendra, 

 from the peripheral portion of the vascular cylinder, and pass very gradually obliquely 

 outwards until they reach the outer cortex, where they bend outward more rapidly to 

 the sporophylls. 



