XXXV] PHYSOSTOMA 309 



in other genera a loose sheath or cupule surrounded the ovule, 

 while in Gnetopsis a similar envelope enclosed two to four seeds. 



The microspores are multicellular and smaller than those of 

 Trigonocarpales, the average dimensions (Conostoma, Physostoma, 

 Lagenostoma) being 67 /x x 52/>i. 



Genera. Physostoma ; Conostoma ; Sphaerostoma ; Lageno- 

 stoma ; Gnetopsis. 



Lagenostoma may safely be referred to Lyginopteris , and 

 Sphaerostoma with but little risk of error to Heterangium: the 

 parent-plants of the other genera are unknown, but all may be 

 regarded as the seeds of Pteridosperms and probably of genera 

 more nearly allied to the Lyginopterideae than to the Medulloseae. 

 The genus Lagenospermum, recently instituted by Nathorst 1 , is 

 dealt with in Chapter xxxi. 



Physostoma. Williamson. 

 Physostoma elegans Williamson. 



The generic name Physostoma 2 was applied by Williamson 3 

 to a seed from the Lower Coal Measures of Lancashire which 

 he named P. elegans ; he afterwards described it as Lageno- 

 stoma physoides, but the original name has been revived by 

 Oliver 4 to whom our knowledge of this type is chiefly due. 

 The specimens figured by Williamson 5 as Sporocarpon ornatum 

 also belong to Physostoma elegans. The seeds are circular in 

 section, approximately 6 mm. long with a maximum diameter 

 of 2 mm. The testa has about 10 longitudinal ribs passing in the 

 apical region into a ring of free lobes or tentacles surrounding and 

 considerably overtopping the nucellar apex: these tentacles 

 take the place of a micropylar tube (fig. 494, I ; fig. 493, D) and 

 are a feature 'in which this seed differs from all other known 

 seeds, fossil or recent 6 .' A single vascular strand passes through 

 the chalazal region and divides into 10 bundles, one to each 



1 Nathorst (14) p. 29. 



2 (Dvaad), to blow; (f>vaa, a bladder. 



3 Williamson (76) p. 160; (17) B. p. 241, PI. xi. figs. 77, 78; PI. xii. fig. 79. 



4 Oliver (09); Oliver and Salisbury (11) passim; Salisbury (14) p. 74. 



5 Williamson (80) A. PL xvn. figs. 2428; (83 2 ) A. PI. xxxi. fig. 27 (called 

 in this case Sporocarpon anomalum, no doubt a slip of the pen). 



6 Oliver (09) p. 75. 



