XXIX] 



SPHAEROSTOMA 



79 



associated with Heterangium Grievii almost amounts to demon- 

 stration of continuity between vegetative organs and seeds. 



Sphaerostoma ovale (Williamson). 



In 1877 Williamson described some detached petrified seeds 

 irom the Lower Carboniferous rocks of Fifeshire, Scotland, as 

 Conostoma ovale and C. intermedium. Dr Benson's investigation 1 

 of these two forms leads her to confirm Williamson's doubts as 

 to the validity of a specific separation and she assigns the single 



FIG. 414. Sphaerostoma ovale. A. Longitudinal section showing the cupule, c, 

 integument, e, f, with vascular bundle, v, the upper part of the nucellus, n, 

 and megaspore, ra; a, archegonia. B. Transverse section through the roof 

 of the pollen-chamber, pc, and the summit of the nucellus. n. (After Benson.) 



type to the new genus Sphaerostoma. The seeds are always 

 associated with the vegetative organs of Heterangium Grievii. 

 In 1909 Oliver 2 expressed the opinion that the Burntisland species 

 of Conostoma (= Sphaerostoma) is probably the seed of Heterangium. 

 The seed consists of a central body representing the nucellus, an 

 inner integument, and an enveloping cupule or outer integument : 

 most specimens have lost the cupule and in this condition they 

 are 3-5 mm. long with a maximum breadth of 2-2 mm. In the 



Benson (14). 



2 Oliver (09) p. 111. 



