390 EQUISETALES 
stated by Scott:! he remarks that “the Calamite, so far as anatomy goes, 
is simply an Zguisetwm with secondary thickening.” The secondary increase 
commences at the nodes, and extends thence through the internodes. 
This again adds point to the similarity with Agwzsetwm, since the trace of 
secondary increase present in Zgudsedum is seen at the nodes, though it 
does not extend into the internodes. The result of the secondary growth 
in Calamites may be a woody mass of great bulk, and varying in the 
details of its structure: into these matters it is unnecessary to enter here: 
it will suffice to quote further from Scott? that “‘we may therefore express 
the general characteristics of the Calamarian vascular system by the state- 
ment that the whole arrangement is of the type of Egudsefum but more 
varied, and sometimes more complex”; and, further, that? “the position 
of the branches with reference to the nodes and leaf-traces was precisely 
the same in Calamites as in the recent Lguisetum.” Thus, as regards 
stelar problems the two stand together, and the hypothesis put forward 
by Gwynne-Vaughan for the elucidation of the stelar structure in Egzzsetum 
should find its application in Calamites also. It will now be shown that 
certain facts derived from these fossils strongly support it. 
In his Pfanzen-palacontologie (p. 205) Potonié established a comparison 
between the secondary vascular tissues of the Calamarieae and the Spheno- 
phyllaceae by mentally doing away with the central mass of primary 
xylem that exists in the latter. Gwynne-Vaughan suggested that by 
inverting this procedure, and considering it possible that the ancestors 
of Eguisetum may have possessed a xylem that extended to the centre of 
the stem, one is led to derive their structure, as it exists at present, 
from the modification of a stele with a solid central mass of centripetal 
xylem such as that of Sphenophyllum or of certain Lepidodendreae. To 
illustrate the nature of the modifications that such a stele would have to 
undergo, a series of parallel developments was pointed out by Gwynne 
Vaughan within the latter group, viz. Lepidodendron Rhodumnense, Selaginotdes, 
Harcourtit, Sigilaria spinosa, and Menardi: here parenchyma appears in 
the xylem, and gradually increases in quantity until only an attenuated 
peripheral ring of xylem remains, which then becomes more or less broken 
up into separate strands. This suggestion raises the question whether any 
Calamarian stem is known in which the hypothetical primary xylem is 
better represented, and is shown to be centripetal in its development? 
At the very same meeting at which Gwynne-Vaughan developed his 
theory Scott described a new species, Calamites pettycurensis, which gave 
the requisite answer. It comes from the Calciferous sandstone of Burnt- 
island.« The interest depends on the fact that each vascular bundle 
possesses a distinct arc of centripetal wood on the side next the pith. 
The carinal canals are present as in an ordinary Calamite, and contain, as 
usual, the remains of the disorganised protoxylem. They do not, however, 
1 Studies, p. 23. 2 Lites Po 25) 
* L025, ps 31. 4Scott, Br7t. Ass. Report, 1901, p. 849. 
