1062 
de Fr aine. — On the Structure and 
conclusive evidence to show that they were in any way connected with the 
original central cylinder ; it is possible that they have arisen later and 
independently of it. Their function is evidently to provide an increased 
water-storing and conducting tissue for the plant, and it is suggested that as 
radial increase progressed in response to the increased physiological require- 
ments, the increased vascular needs were provided for by extrafascicular 
arcs and strands which arose independently in the cortex, and which are not 
therefore to be derived by reduction from a system of steles. From such 
a type as Sutcliffia , which may be regarded as the most primitive member 
of the Medulloseae at present known, it is suggested that two divergent lines 
may have arisen. The one advanced with increasing complexity in the 
direction of multiplication of the number of steles, through some such form 
as Medullosa anglica , and ended blindly in the more complex Medulloseae, 
the extraordinary complexity of the series of steles and the anastomosing 
medullary and cortical c star rings * possibly proving too cumbrous and not 
sufficiently plastic to allow of further evolution along these lines. The other 
maintained the protostelic condition, and advanced by further modification 
of the single vascular cylinder, and perhaps by the elaboration of the extra- 
fascicular arcs and accessory vascular strands of the cortex, in the direction 
of the Cycadales. 
It is to be hoped that the discovery of further fossil forms may shed 
additional light on this question, for the evidence connected with the repro- 
ductive organs which is at present available, tends to show that the 
Medullosean seeds such as Trigonocarpus and Stephanospermum are in sub- 
stantial agreement in certain respects with the genera of living Cycads . 1 
And in this connexion it may be noted that the recent investigation of the 
ovule of Bowenia spectabilis by Kershaw 2 shows that as regards structure, 
and development of the pollen-chamber, ‘ the closest parallel to the Cycads 
among fossil seeds is to be found in seeds of the Trigonocarpus affinity, and 
there seems to be no evidence in either of them that this structure had 
resulted from simplification of a more complicated type, such as that of the 
Lagenostomales.’ Kershaw further points out that not only in the pollen- 
chamber, but also in respect of the integument and vascular supply, there is 
a very close connexion between Cycadean seeds and those of the Medulloseae. 
Further, as Scott 3 has already shown, £ the structure of the petiole and 
the organization of the leaves generally are very similar in Medulloseae and 
Cycadaceae.’ 
1 Oliver, F. W., and Salisbury, E. J. : On the Structure and Affinities of the Palaeozoic Seeds 
of the Conosloma Group. Ann. of Pot., vol. xxv, 1911, p. 40. 
Scott, D. H., and Maslen, A. J. : The Structure of the Palaeozoic Seeds, Trigonocarpus Parkinsoni 
Brongniart, and Trigonocarpus Oliveri , sp. nov., Part I. Ann. of Bot., vol. xxi, 1907, p. 115. 
2 Kershaw, E. M. : Structure and Development of the Ovule of Bowenia spectabilis. Ann. of 
Bot., vol. xxvi, July, 1912. 
3 Studies, loc. cit., p. 649. 
