122 MEDULLOSEAE [CH, 



the integument 1 . The micropyle is triangular in section and may 

 exceed in length the whole seed (figs. 425; 426, A). Its form 

 as seen in transverse section (fig. 426, B) suggests the presence 

 of wings : this appearance may be deceptive and due to pressure 

 or, more probably, it represents an original feature. The seed- 

 body, that is the portion enclosed by the integument, consists 

 of the nucellus, represented by a few crushed layers of cells,, 

 bounded by a well-defined epidermis; the nucellus is separated 

 from the integument from the base of the seed upwards, an 

 important feature in which this and some other Palaeozoic seeds 

 differ from Lagenostoma and the seeds of recent Cycads which 

 are characterised by an integument adnate to the nucellus up 

 to the level of the shoulder ; the seeds of the Conifer Phyllodadus 

 afford an example of separation of integument and nucellus as 

 in Trigonocarpus. The innermost layer of the nucellus consists 

 mainly of tracheal tissue investing the large megaspore (fig. 426, 

 A, C, m) which is preserved as a contracted membrane detached 

 from the nucellus after the death of the seed. At the summit 

 of the nucellus is a relatively small pollen-chamber (fig. 426, A, PC) 

 like a broad and low cupola bearing a terminal beak which extended 

 some distance into the micropylar tube. No microspores have 

 been found in this species, but Oliver 2 records the occurrence of 

 multicellular microspores in Trigonocarpus pusillus. The pedicel 

 of the seed had a central strand of sclerous tissue penetrated by 

 a concentric vascular bundle which gives off six strands to supply 

 the sarcotesta (fig. 426, C, v) and then passes into the nucellus 

 where it forms a tracheal sheath (fig. 426, A, nt) surrounding the 

 lower part of the megaspore and at a higher level breaks up into 

 anastomosing strands of tracheids which reach up to the plane of 

 insertion of the pollen-chamber. 



A second species described by Scott and Maslen as Trigono- 

 carpus Oliveri has been further investigated by Salisbury who finds 

 that it is an 8-angled seed which cannot be retained in the genus 

 Trigonocarpus: its systematic position 'must for the present 

 remain uncertain 3 .' Dr Arber has recently described a new species 

 of Trigonocarpus, T. Moyseyi*, from the Nottingham Coal-field 



1 Arber, A (14). 2 Oliver (04) p. 97. 



3 Salisbury (14) p. 65. 4 Arber, E. A. N. (14) p. 95, PL vi. fig. 1. 



