1064 
de Fr aine. — On the Structure and 
system, the origin and behaviour of the c meristeles ’, the leaf-trace bundles, 
and the close agreement in histological details. 
It is provisionally attributed to 5 . insignis because the features which 
characterize the stem (i. e. the secondary tissues, the extrafascicular arcs, 
the secondary cortex, and the absence of leaf-bases) are considered to 
be most probably due to age of the plant. 
3. Theoretical conclusions (Section VIII, pp. 1058-63). It is suggested 
that the origin of the Cycadaceae is to be sought along the Medullosean 
line from some such genus as the protostelic Sutcliffia , the central cylinder 
of the Cycads being probably derived from the protostele by the gradual 
disappearance of the primary internal tracheides. The extrafascicular arcs 
and accessory vascular strands are regarded as homologous in Sutcliffia , 
Medullosa, and the Cycads ; they are not considered to be derived by 
reduction from a system of steles, but to have arisen independently of the 
central cylinder, possibly in response to increased physiological require- 
ments. 
It is suggested that two divergent lines may have arisen from some 
such primitive type as Sutcliffia , as follows : 
Sutcliffia type ' 
— ► Medullosa anglica -* more complex Medulloseae (blind ending). (Through 
increasing complexity in the number and arrangement of the steles.) 
► Cycadales. (Through 
modification of the protostele and elaboration of the extrafascicular zones.) 
Literature. 
Bertrand, E. C., et Corneille, F. : La masse libero-ligneuse elementaire des Filicinees actuelles. 
Trav. et M^m. de PUniversitd de Lille, 1902, t. x, Mem. no. 29. 
Chodat, R. : Les Pteridopsides des temps paleozo'iques ; etude critique. — Arch, des Sci. phys. et 
nat., Geneve, t. xxvi, 1908. 
Compton, R. H. : An Investigation of the Seedling Structure in the Leguminosae. Journ. Linn. 
Soc. (Bot.), vol. xli, June 28, 1912. 
Corneille, F., see Bertrand et Corneille. 
de Fraine, E. : On the Seedling Structure of Certain Cactaceae. Ann. of Bot., vol. xxiv, 1910. 
: see Hill and de Fraine. 
Farmer, J. B., and Hill, T. G. : On the Arrangement and Structure of the Vascular Strands in 
Angiopteris evecta and some other Marattiaceae. Ann. of Bot., vol. xvi, 1902. 
GoPPERT und Stenzel : Die Medulloseae, eine neue Gruppe der fossilen Cycadeen. Palaeonto- 
graphica, 1881. 
Gregg : Anomalous Thickening in the Roots of Cycas Seemanni. Ann. of Bot., vol. i, 1887. 
Hill, T. G. : On the Seedling Structure of Certain Piperales. Ann. of Bot., vol. xx, 1906. 
: see Farmer and Hill. 
and de Fraine, E. : On the Seedling Structure of Gymnosperms. III. Ann. of Bot., 
vol. xxiii, 1909. 
