308 LAGENOSTOMALES [CH. 



well-marked anatomical features and probably Cordaitean; it 

 has, however, been shown that typical Platysperms were also 

 borne on leaves of Pteridosperms and, as Mrs Arber 1 says, the 

 notion that every member of the Platyspermeae was necessarily 

 a Cordaitean seed has been discredited by the discovery of the 

 seeds of Aneimites (Wardia) and Pecopteris Pluckeneti 2 . For 

 general purposes it is hardly necessary to adopt the subdivisions 

 of the Lagenostomales used by Oliver and Salisbury 3 , though as 

 facts accumulate we shall no doubt be able to make further 

 advances towards a natural system of classification. The following 

 three divisions of Permo-Carboniferous seeds include genera 

 founded on petrified specimens and thus afford valuable morpho- 

 logical data. The groups Lagenostomales and Trigonocarpales 

 include types belonging to closely related plants, a relationship 

 clearly expressed in the seed-characters. 



I. LAGENOSTOMALES. 



The seeds included in this group are for the most part Radio- 

 sperms, but in its slightly developed bilateral symmetry Conostoma 

 oblongum is a type transitional between Badiosperms and Platy- 

 sperms. The testa may be ribbed and the ribs vary in number. 

 The nucellus (megasporangium) is united to the integument not 

 only at the base but laterally as far as the shoulder of the seed up 

 to a level corresponding to the base of the pollen-chamber (lageno- 

 stome) as in all recent Cycads and in the majority of Conifers. 

 The seeds proper apart from the cupule are supplied with a single 

 set of vascular bundles ; there is no vascular tissue in the nucellus, 

 a feature no doubt correlated with the fusion of nucellus and 

 integument 4 . The free portion of the integument is more or less 

 deeply lobed or, in Lagenostoma, it forms a pyramidal canopy 

 of fused lobes enclosing the lagenostome. The presence of a 

 tapetal zone surrounding the megaspore is believed to be a feature 

 characteristic of the group 5 . The testa, wholly or partially 

 ribbed, is relatively thinner than in the Trigonocarpales and 

 Cardiocarpales, and in its differentiation agrees less closely with 

 the testa of recent Cycadean seeds. In Lagenostoma and possibly 



1 Arber, A. (10) p. 505. 2 See Chapter xxxi. 



3 Oliver and Salisbury (11). 4 Salisbury (14) p. 67. 



5 Oliver (09), p. 99. 



