1043 
Affinities of Sutcliffa. 
concentric bundle, partially or completely surrounded with secondary 
tissues, leaves the stele — the main stele repeated on a small scale. In the 
new Sutcliffia this strand divides more or less unequally into smaller strands, 
of which the primary wood breaks up ultimately into concentric leaf-trace 
bundles, the secondary tissues being lost during the process. In Medullosa 
anglica the strand passes gradually outwards, and then divides up into 
collateral leaf-trace bundles, the secondary tissues also being lost during 
the breaking-up process. 1 
On the grounds of the additional evidence afforded by the new stem it 
woidd appear justifiable to regard Sutcliffia as possessing for its main vascu- 
lar axis a protostele , from which was given off vascular strands varying in 
size , but in every case similar in structural details to the protostele ; these 
strands divided irregidarly into smaller bundles which were ultimately com- 
pletely used up in the production of leaf- trace bundles . This interpretation of 
the structure connects the fossil more closely with the genus Medullosa through 
such a type as M. anglica, and still further supports Scott s view of its 
primitive position in the Medidloseae. 
IV. Histology. 
i. Structure of the Wood. The structure of the primary wood is in all 
essential characters similar to that of Sutcliffia insignis , as can be seen by 
comparing Text-figs. 
6 and 7, which repre- 
sent portions of the 
primary wood of each 
drawn on the same 
scale. The tracheides 
are of the ordinary 
elongated form, with 
multiseriate bordered 
pits on the radial 
walls ; they are of 
large size, varying in 
diameter from 316 to 
400 /x, the average 
being about 281 /x ; 
their size is thus 
slightly greater than 
in S.insignis, in which, 
though the diameter 
may reach 350 /x, the range lies between 170 and 320 /x. 
Text-fig. 10. Part of a radially symmetrical leaf-trace bundle, 
x 70. s.c. = secretory elements; xy r = primary xylem ; par. = 
parenchyma. 
1 Scott, D. H. : On the Structure and Affinities of Fossil Plants from the Palaeozoic Rocks. 
III. On Medullosa anglica , a New Representative of the Cycadofilices. Phil, Trans. Roy. Soc., 
Ser. B, vol. cxci, 1899, P* 9 2 * 
