112 THE EVOLUTION OF PLANTS 



of which Lyginodendron is an example, the name 

 Pteridospermese (Seed-ferns) has been adopted. 



One or two other examples of Pteridosperms 

 may be given. The first case in which a seed was 

 found in actual connection with a "Fern frond" 

 was that of Neuropteris heterophylla, in which, 

 in 1904, Mr. Kidston discovered large seeds, of 

 the size of a hazel-nut, attached to a stalk which 

 still bore the characteristic leaflets of the plant. 

 The fronds of this "Fern" were of enormous 

 size, comparable to those of the largest Tree- 

 ferns, and hi form somewhat resembled a gigantic 

 Osmunda. 



The family to which Neiiropteris belonged is 

 pretty well known, and a great variety of seeds 

 have been referred to these plants, though the 

 evidence is nowhere else so direct as in Mr. 

 Kidston's species. They were mostly plants of 

 large dimensions and rather like Tree-ferns in 

 appearance, their trunks sometimes reaching a 

 thickness of about two feet. The structure of 

 the stem was peculiar, for instead of there being 

 a single column of wood, as in all ordinary trees, 

 there were here several such cylinders in the 

 stem, each surrounded by its own zone of bast and 

 growing in thickness by its own cambium. The 

 many-cylindered structure is common in the stems 

 of Ferns, as can be seen by cutting across the 

 creeping stem of a Bracken-fern, but the com- 



