Affinities of Sntcliffia. 1063 
Hence, at the present time, the balance of evidence drawn from both 
the vegetative and reproductive features favours the view of the Medullosean 
ancestry of the Cycads, 1 through some protostelic form. 
IX. Summary. 
1. Structural facts (Sections II-VI, pp. 1033-56). The specimen 
consisted of a stem of large size and considerable complexity of structure. 
The vascular system was composed of a protostele, from which large leaf- 
trace strands (‘ meristeles ’) were given off. These large leaf-traces divided 
up into smaller ones and were finally completely used up in the formation 
of either unilateral or radially symmetrical concentric foliar traces. 
The vascular strands of all orders, with the exception of the ultimate 
foliar traces, were surrounded by a wide zone of secondary tissue. 
Extrafascicular bands of wood and bast formed a network round 
the stele and large leaf-trace strands ; they showed occasional inverse 
orientation. Accessory vascular bundles also occurred. 
A wide, irregular, discontinuous zone of secondary cortex surrounded 
the greater part of the stem ; it lay immediately outside the vascular 
structures. 
The primary xylem consisted of tracheides intermixed with xylem- 
parenchyma ; the protoxylem, which frequently occurred in paired groups, 
was in all cases exarch. 
The primary and secondary tracheides both showed multiseriately 
arranged bordered pits on the radial walls ; the protoxylem consisted 
of spirally marked elements. 
Short, broad, isodiametric tracheides occurred on the inner edge of the 
xylem of the extrafascicular strands, and occupied the central region of the 
accessory vascular bundles. 
The phloem of the leaf-traces contained a ring of large elements, 
probably of the nature of sieve-tubes. The secondary phloem in all cases 
consisted of strands of narrow, apparently thick-walled elements, embedded 
in parenchyma. 
The 6 pericycle ’ and cortex have abundant secretory elements varying 
very much in size ; in some cases the contents are preserved in the form of 
black carbonaceous matter, others present a vacuolated appearance. 
The concentric foliar bundles were partially surrounded by strands 
of fibrous elements. 
2. Attribution (Section VII, pp. 1056-8). The stem is included in 
the genus Sntcliffia on account of the general structure of the vascular 
1 Compare with the tentative statement in Studies, p. 650. 
