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ON THE GENUS KNORRIA, Stemb.
By W. Carruthers, F.L.S., E.G.S.
(Plate XCIIL)
This genus was established by Sternberg, in the ' Tentamen Florae
Priraordialis ' (p. xxxvii.), which accompanied the first volume of his
' Flora der Vorwelt,' for two stems which he considered to be dico-
tyledonous, and to have been clothed with fleshy cylindrical leaves,
like some succulent plants. The fossils were casts found in beds be-
longing to the Coal-measures. Stems that are imbedded in sandstone
have frequently entirely perished, and the cavity remaining having been
afterwards filled in with amorphous material, there is no indication of
the fossil except this cast of the original, which shows often in tiie most
perfect manner all the external characters of the stem, but without
any trace of its internal structure. As a consequence, considerable
uncertainty has always existed, as to the true nature of these fossils.
They are described as decorticated stems, without any definite mean-
ing being attached to the term ' decorticated.'
Professor "Williamson has clearly established that some Sternbergias
are the casts of the medullary axis of Dadoxylon. Endogenites striata of
Lindley and Hutton is a similar cast of that or an allied coniferous
genus. The most familiar condition of Catamites, as a fluted and con-
stricted stem, is in like manner only the cast of the medullary or cel-
lular axis ; the thin incrustation of coal wliich is attached to it when
it is removed from the rocky matrix, representing the greatly altered
woody tissue. Knorria also is the cast of the interior of a Lepido-
dendroid stem, as was at first supposed by Sternberg, though he after-
wards changed his opinion, and by many subsequent writers as Gceppert,
Dawson, etc. It has been described by these authors as " decorti-
cated." In the stems mentioned, with the exception of Knorria, the
" cortex " means the whole of the woody tissue, as well as the cortex
properly so-called. In Lepidodendron, however, the wood is a very
slender cylinder in the centre of the stem, while the casts of Ktiorria
have a considerable diameter. A specimen from the Coal-measures,
near Edinburgh, for which I am indebted to Charles Peach, Fsq., whose
long-educated eye appreciated its value, exhibits the relation of the cast
to the complete stem. In the lower part of the specimen, the short
VOL. VII. [jULY 1, 1869.J N