Relation of Pteridosperm Anatomy to that of Cycads. 67 
alternative view that the central cylinder of a Cycadean stem may 
have been derived from a protostelic type such as Sutcliffia, the 
internal tracheides having been gradually lost. The extrafascicular 
zones and accessory cortical strands of some Cycads occur also in 
Sutcliffia and Medullosa, but it is at present impossible to determine 
whether they are connected with the original central cylinder, or 
whether they have arisen secondarily to meet physiological needs. 
Miss de Fraine considers that from such a primitive type as 
Sutcliffia two divergent lines of evolution may have arisen. The 
first line proceeded through fairly simple types like Medullosa anglica 
to complex types with numerous steles, and here ended blindly, 
for these types were evidently insufficiently plastic for further 
evolution to take place. The second line remained protostelic 
throughout, the original vascular system becoming modified and 
giving rise to the Cycadean type. In the case of polyxylic Cycads, 
the so-called anomalous vascular structures may have been derived 
by the elaboration of the extrafascicular arcs and accessory vascular 
strands of the ancestral type. Or, it might be suggested that in those 
recent Cycads which exhibit extrafascicular formations, it is merely 
a case of the expression of tendencies inherited from an ancestor 
which also gave rise to lines exhibiting the character constantly. 
Miss de Fraine’s view is interesting in that it derives Cycadean 
anatomy from a monostelic form very similar to Heterangium, the 
basal form of the line through which it has its origin according to 
Dr. Scott, who himself suggests the probability of a common origin 
of the Lyginopterideae and Medulloseae “ from a point not very far 
below the level of stems such as those of Sutcliffia and Heterangium.” 
So that since the discovery of Sutcliffia, which connects the two 
lines anatomically, the divergent theories of Scott and Worsdell 
are, to a certain extent, brought together by that of Miss de Fraine. 
Also, the discovery of Sutcliffia adds further interest to the 
conclusion previously arrived at by Matte, to the effect that the 
Cycads were derived from the Lyginopterideae or a nearly related 
family through the Medulloseae. The existence of Sutcliffia to a 
certain extent, justifies this view, since it shows how nearly related 
are the two main groups of Pteridosperms. 
From the evidence at present before us, it seems safe to suggest 
that the Lyginopterideae and the Medulloseae have arisen from a 
basal stock, giving origin also to the Cycadean line, this passing at 
least close to the simpler forms of the Medulloseae. 
Botany School, Cambridge. December, 1913. 
