The Filicinean Vascular System . 
37 
Filicinean vascular system. Sutcliffia, Medullosa , Colpoxylon, 
Cladoxylon, Ptychoxylon, all tried secondary thickening in con¬ 
junction with more or less unwieldy primary systems, mostly 
clumsy imitations of fern-types. In most of them the secondary 
tissues of one cylinder or part of a cylinder came into collision, so 
to speak, with those of another. In none is the primary tissue 
confined to the simple circle of leaf-traces and compensation strands, 
which is the condition for rapid growth of the primary shoot, estab¬ 
lished and made good by the zone of secondary wood. It may be, as 
Worsdell supposes, that the Medullosa- type, by means of a drastic 
reduction, had a partial success in the evolution of the Cycad-type, 
thus arriving at a similar arrangement by another route. 
The vascular structure described, together with the evolution of 
the seed, and the ultimate acquirement of siphonogamy and 
angiospermy, may be regarded as marking the final stage in the 
long process of progressive adaptation to terrestrial life, and as 
providing the equipment necessary to the attainment of that 
complete dominance of world-vegetation reached by the modern 
dicotyledonous tree. 
GLOSSARY 
of the principal terms used in these lectures 1 elating to the con¬ 
struction of the stelar system, with references to their original use. 
Haplostele. The cauline vascular cylinder in its simpler form, in 
which the centre is occupied by xylem, and this 
is typically surrounded by phloem, pericycle and 
endodermis. (Brebner ’02). 
Protostele. A haplostele which is assumed to be primitive. 
(Jeffrey ’97). 
Amphiphloic protostele (or haplostele) = The Lindsaya- type of 
stele. A stele in which the solid central xylem 
is traversed by a continuous internal strand of 
phloem, connecting with the external phloem at 
the nodes. (Chandler ’05: see also Tansley and 
Lulham ’02). 
Solenostele (as defined by Gwynne-Vaughan). A stele in which 
the vascular tissue is arranged in a hollow 
cylinder with phloem and phloeoterma on either 
side, the complete continuity of which is inter¬ 
rupted only by the departure of the leaf-traces ; 
the gaps thus produced being closed up in the 
internode above before the departure of the next 
