190 



D. H. Scott. 



VI. Pteridospermeae. 



Id reviewing the attenuated ranks of the Palaeozoic Ferns, it 

 has often been necessary to refer to the contemporary^ Fern-like 

 Spermophyta which have so largely displaced them. We have now 

 to consider, as briefly as may be, the evidence we possess as to the 

 nature and extent of the Pteridospermeae, and the justification of 

 their existence as a distinct class of plants. I do not propose to trace 

 historically the growth of our knowledge, w^hich, though an interesting 

 theme, would occupy us too long, but rather to attempt a concise 

 statement of the present position of the question. I will begin with 

 the Lyginodendreae, the type-member of wiiich, Lijginodendron old- 

 hamium, has now been investigated in all its parts. 



Lyginodendreae. 



The stem of Lyginodendron oldhamium (discovered bj' B i n n e y in 

 1866, but first fully described by Williamson in 1873) presents a 



Fig. 18. Lyginodendron oldhamium. Trans, section of stem, showing pith, primary 



xylem-gronps, secondary xylem, phloem, pericycle and cortex. The leaf-trace bundles 



are seen ontside the wood. X abont 2''2- 



