CYCADOFILICALES 37 



in the vegetative organs. Between the secretory zone and the embryo 

 sac, and entering into the cap of the sac within the pollen chamber, 

 is a region of six or more radially compressed layers of cells, which 

 is regarded as a "tapetum," but which may be only the region of the 

 nucellus compressed by the enlarging embryo sac. 



The Lagenostoma group. —Associated with Lagenostoma and 

 Physostoma there is the seed genus Conostoma (3), and also the recently 

 announced genus Sphaerostoma (83), based upon Williamson's 

 Conostoma ovale and the oldest paleozoic ovule known structurally. 

 These four genera form what may be regarded as a natural group, 

 belonging to the Lyginodendrineae. Lagenostoma Lomaxii alone, 

 of the petrified seeds of this group, is definitely connected with a 

 species of Lyginodendron {L. Oldhamium); while L. Sinclairii and 

 L. Kidstonii (Physostoma Kidstonii) are impressions which are con- 

 nected with foliage of the Sphenopteris type. Lagenostoma ovoides, 

 Physostoma elegans, and Conostoma all occur as petrifactions, but 

 they have not been referred to definite species of Sphenopteris or of 

 Lyginodendron. It had been inferred from association that one of 

 the species of Conostoma might be the seed of Heterangium, and now 

 Miss Benson (83) has shown it to be probable that the new seed 

 genus Sphaerostoma {Conostoma ovale) belongs to Heterangium 

 Grievii. 



In 1885 Renault (9) described Gnetopsis elliptica, in which there 

 are four seeds (two often abortive) inclosed in a cupule consisting of 

 two partly fused bracts, each of which becomes five-toothed above. 

 The integument expands around the micropyle and forms a chamber, 

 and bears two long feathery appendages. There is a central core 

 of tissue within the pollen chamber, and the neck of the cham- 

 ber divides into lobes. The endosperm and two distinct archegonia 

 are preserved. The two fused bracts doubtless suggested to Renault 

 a relationship to Gnetales, but the general structure is much more 

 suggestive of a seed of the Lagenostoma type (87). 



The four seed genera feferred to agree in the amount of freedom 

 of nucellus and integument, in the peculiar character of the pollen 

 chamber with its projecting beak, in the composition of the free por- 

 tion of the integument (distinct lobes to lobes "fused"), in the cover- 

 ing of mucilage hairs, in the distribution of the vascular strands, and 



