LYGINODENDRON 357 



We will begin our account of the Pteridosperms 

 with the family Lyginodendreae and the genus Lygino- 

 dendron, the type species of which now has the 

 distinction of being the most completely known of all 

 fossil plants (see Fig. 1, Frontispiece). 



I. LYGINODENDRON 



The species, or rather, perhaps, group of species, with 

 which we are concerned at present is that named by 

 Williamson Lyginodendron oldhamium} Although the 

 plant was first described by Binney, in 1866, it is 

 mainly to Williamson's work that our present, very 

 thorough knowledge of its vegetative structure is for 

 the most part due. Fortunately, specimens of Lygino- 

 dendron oldhamium are among the very commonest 

 remains contained in the calcareous nodules of the 

 English Coal-measures ; their preservation is often 

 wonderfully perfect, so the material for investigation 

 is altogether favourable. 



The vegetative anatomy will be first considered, thus 

 following the historical order in the progress of our 

 knowledge, and subsequently the recently discovered 

 seeds and male organs will be dealt with. 



Both foliage and roots are now well known, and we 

 are able to form a fairly accurate idea of the habit of 

 the plant (see Fig. 1, Frontispiece). We will begin 

 our description with the stem, the part to which the 

 name Lyginodendron oldhamium was first applied, 



1 For nomenclature see Williamson, ' ' Organisation of the Fossil Plants 

 of the Coal-measures," Part iv., Phil. Trans. 1873, p. 377; also 

 Williamson and Scott, " Further Observations, etc.," Part iii., Phil. 

 Trans. 1895, B, p. 705. Potonie' has re-named the genus Lyginopteris. 

 See his Lehrbttch der PJlansen-palaontologie, Leipzig, 1898, p. 160. 



