XXX 



XV] POLYLOPHOSPERMUM 329 



was formed: in the case of S. akenioides Oliver considers that 

 fertilisation was not assisted by the production of a pollen-tube. 

 The two cells by further division gave rise to a secondary cell- 

 complex consisting of at least eight antherozoid-mother-cells. 

 No antherozoids have been found in the microspores but it is 

 possible that two small bodies, 17//, x 15//,, met with in a pollen- 

 chamber may represent the nuclei of sperms. Their small size 

 differentiates them from the much larger male gametes of Cycads 

 and from the supposed sperms of Physostoma and Lagenostoma. 



We have no proof as to the nature of the plant which bore 

 seeds of the Stephanospermum type, but it is significant that the 

 specimens occur in close association with fragments of Alethopteris 

 and Myeloxylon, a circumstance that favours the view, based on 

 the resemblance of these seeds to Trigonocarpus, that Stephano- 

 spermum is the seed of a member of the Medulloseae. 



Polylophospernmm 1 . Brongniart. 



The type-species Polylophospermum stephanense Brongn. 2 , 

 founded on partially preserved material from Grand'Croix, is 

 a narrow hexagonal seed 15 mm. long. Additional facts as to 

 the structural features have been contributed by Oliver 3 . The 

 testa is differentiated into an inner shell (sclerotesta) and an 

 outer flesh (sa, fig. 495, C, D) : the sclerotesta has six prominent, 

 fissured, ribs, one at each angle, and between these are six solid 

 and less prominent secondary ribs. Oliver states that there is 

 an outer series of vascular bundles in the sarcotesta, one bundle 

 immediately external to each secondary rib (fig. 495, C, v). In 

 the presence of two kinds of ribs and in the relation of ribs to 

 tracheal strands Polylophospermum agrees with Trigonocarpus 

 Parkinsoni. Strands of short tracheids supply the peripheral region 

 of the nucellus and, as in Stephanospermum, reticulate elements 

 extend as far as the floor of the large pollen-chamber. There 

 was probably no lateral union between nucellus and integument. 

 A striking feature is the prolongation of the testa at each end 

 of the seed to form an open chamber surrounding the micropylar 

 beak and the seed-base (fig. 495, D, s, s) : the apical chamber, 



1 X60os, a ridge. 



2 Brongniart (74) p. 256, PI. xxm. figs. 68; (81) PI. C, figs. 68, 



3 Oliver (04 2 ) B. PL n. figs. 510; (07) fig. 1. 



