XXIX] HETERANGIUM 71 



of strands of large reticulately pitted tracheids intermixed with 

 parenchyma and exhibiting structural features differing apparently 

 from those of any known type. Corda's material has been 

 re-examined by Kubart 1 who figures a section from it. Heteran- 

 gium is a genus closely allied to Lyginopteris both in habit and in 

 general anatomical characters. The stem is monostelic ; the 

 vascular cylinder prior to secondary thickening resembles the 

 protostele of certain recent species of Gleichenia and may be com- 

 pared also with Trichomanes scandens 2 . It agrees with that of 

 Lyginopteris in the possession of primary mesarch bundles but 

 differs in the substitution of a cauline axial mass of metaxylem 

 for the pith of Lyginopteris. The secondary vascular tissue agrees 

 closely with that of recent Cycads and Lyginopteris. A character- 

 istic feature is the occurrence of numerous horizontal bands of 

 sclerous cells in the cortex (fig. 412) of the stem and in the ground- 

 tissue of the rachis and larger branches of the fronds. The stem 

 was erect and rarely branched ' giving off large foliar appendages 

 at somewhat distant intervals and from its entire circumference' 3 . 

 Our knowledge of the reproductive organs is less precise than in 

 the case of Lyginopteris ; but we are justified in asserting that 

 Heterangium, is a Pteridosperm which in all probability bore fern- 

 like microsporangia and seeds similar in general plan to Lageno- 

 stoma. 



The association of some seeds included in Williamson's genus 

 Conostoma with Heterangium Grievii in the Pettycur beds and 

 their resemblance to Lagenostoma, the seed of Lyginopteris, 

 suggested the possibility of actual connexion: further evidence 

 in support of this view has recently been brought forward by 

 Dr Benson 4 in the case of a species of Conostoma which she transfers 

 to a new genus Sphaerostoma. 



The two species Heterangium Grievii and H. tiliaeoides are 

 described in illustration of the genus and reference is made to a 

 few other types. 



1 Kubart (08) fig. 3. 



2 Vol. n. p. 310, fig. 237, C; p. 311, fig. 238. 



3 Williamson (73) A. p. 403. 



4 Benson (14). 



