CYCADOFILICALES 



49 



approximation to the endosperm beak ("tent pole") that occurs among 

 the Cordai tales and in Gingko (85). 



In the Lagenostoma group the megaspore membrane varies from 

 "robust" in Lagenostoma, to very delicate (only occasionally seen) 

 in Physostoma, and indistinguishable in Conostoma (85) ; in Trigono- 

 carpum it is distinct (73). 



THE MALE GAMETOPHYTE 



In the majority of cases the pollen chambers have contained pollen 

 grains in more or less abundance, and these pollen grains, whenever 

 any internal structure is evident, 

 contain a tissue of numerous cells. 

 In Lagenostoma Lomaxii " multi- 

 cellular pollen grains" have been 

 observed (38); and in L. ovoides 

 germinating grains have been 

 found in the pollen chamber (fig. 

 49) associated with bodies inter- 

 preted as sperms (78). These 

 sperms are further interesting in 

 agreeing in form and general 

 appearance with those of living 

 cycads and of Gingko rather than 

 with those of ferns. In Physos- 

 toma elegans (85) the same cell 

 plexus occurs in the much smaller 

 pollen grains (fig. 51), recalling 

 that of Stephanospermum (de- 

 scribed below); and here also 

 certain associated subreniform 

 bodies are interpreted as sperms. 

 In this species a differentiation 

 of the cells in size was observed 

 by Oliver, who suggests that the larger cells, at least, produced 

 sperms, and that the smaller cells might be prothallial. 



In Stephanosperum akenioides (47) numerous pollen grains are 

 constantly found within the pollen chambers, and Oliver succeeded 



Fig. 49. — Lagenostoma ovoides: pollen 

 chamber and contents; nl, portion ol 

 central core of nucellus; nw, wall of nuceU 

 lus; p', p', pi, p% four pollen grains; a, 

 sperm; ai, sperm cut across; e, protru- 

 sion of endospore ; t, tissue probably fungal; 

 X155. — After Miss Benson (78). 



