206 D- H. Scott. 



The evidence for the reference of the seed Trigonocarpon olivae- 

 forme to Medidlosa anglica consists tirstlj', as already mentioned, in 

 the constant association of the petrified seeds with fragments of the 

 plant; further, in the equally general association of corresponding 

 casts of seeds with the foliage of Alethopieris hnchitka. As regards 

 structure, the chalazal and sarcotestal bundles of the seed contain the 

 peculiar, finely scalariform tracheides, characteristic of MednUosa, espe- 

 cially in its foliar bundles (see Scott, 1899, PI. 10. Fig. 5; PI. 12, 

 P'ig. 15), and there is also some agreement between the hypodermal 

 tissues of the sarcotesta and those of the petiole. The attribution 

 in the case of Triiionocarpon is rendered highly probable by Mr. K i d - 

 s ton' s discovery of the seed of Neuropteris heterophylla, and I have 

 little doubt that it is correct, though the direct proof of actual con- 

 tinuity has not so far been obtained. 



A few words may be added on the anatomy and habit of the 

 ]\redulloseae (a family-name which we may provisionally take as 

 synonymous with Xeuropterideae). In the species of MednUosa from 

 the Permian of the Continent, which have long been known, the 

 structure is a good deal more complex than in the more ancient 

 British form. The elaboration consists essentially in the differentiation 

 of a central and a peripheral system of steles, the peripheral system 

 sometimes forming a continuous, or nearly continuous ring. As the 

 secondary growth of the external steles was in some forms much 

 greater on the outer than on the inner side, a certain resemblance to 

 the stems of Cycadaceae wdth medullary bundles is noticeable, ac- 

 centuated in the largest stems of M. stellata by the appearance of 

 extrafascicular zones of wood and bast enclosing the whole stelar 

 system. Some authors, notably Mr. Worsdell\), have laid great stress 

 on these resemblances, which lead them to place the Medulloseae on 

 the line of descent of the Cycads. Personally, I have been unable 

 to convince myself that the stem of the Cycadaceae admits of an 

 interpretation on "polystelic" lines, though on other grounds the 

 affinity suggested has much in its favour. 



While we have in the Permian Medulloseae striking examples 

 of the extreme complexity which this type of stem was capable of 

 assuming, Siddiffla insignis, a plant recently discovered in the Lower 

 Coal-Measures of Lancashire, carries us back to a tj'pe of structure 

 probably more primitive than had previously been known in this 

 family. 2) The stem has a central stele of great size, without pith, 



^) W. C. Worse! ell, The Structure and Origin of the Cycadaceae. Ann. of Bot. 

 Vol. XX, April 1906. A full list of literature is attached to this paper. 



^) Scott, A New Type of Stem from the Coal-Measures. Bot. Centralblatt, 

 Band 101, p. 591, 1906. The full description will appear immediately in the Trans. 

 Linn. Soc. of London. 



