1034 
de Frame.— On the Structure and 
trace of the decurrent leaf-bases which form so distinctive a feature in the 
specimen described by Scott are, in all probability, due to the formation 
of cork, which resulted in the sloughing off of the exterior tissues. In 
the upper sections of the series the beginning of cork cambium formation 
can be traced (see Text-fig. 18, A and B), but in this region, as in the lower 
part of the specimen, the outer tissues are absent. It is possible, of course, 
that as the fragment of stem drifted out to sea , 1 the vicissitudes of the 
journey partly destroyed and tore the more delicate outer tissues, and there 
can be no doubt that some parts of the stem have been injured in this way ; 
Text-fig. 3. Transverse section of a very small concentric leaf-trace strand. x x = primary 
wood ; ph . = phloem ; l.e. = large elements of the phloem ; fs. = fibrous strands ; s.c. = secretory 
cell, x 70. 
at the same time it appears probable that some part of the cortex has been 
lost naturally. The suggestion is put forward that the phellogen was 
a short-lived tissue, and was replaced by successively deeper seated cam- 
biums, a phenomenon which is not uncommon in many vascular plants 
at the present day. Where traces of the cortical tissue are found, here and 
there throughout the series, it is seen to be composed of delicate, thin- 
walled parenchyma cells, with numerous secretory elements scattered 
1 Stopes, M. C., and Watson, D. M. S. : On the Present Distribution and Origin of the 
Calcareous Concretions in Coal Seams, known as Coal ‘ Balls '. Phil. Trans. Roy. Soc. London, 
Ser. B, vol. cc, 1908, pp. 204 and 211, 
