456 STUDIES IN FOSSIL BOTANY 



The seed, with its fleshy and stony coats, double 

 vascular system, and pollen-chamber, is evidently very 

 nearly akin to the seed of a recent Cycad, the chief 

 difference consisting in the free nucellus, whereas in 

 the modern family it is adherent to the integument. 



The petrified specimens of Trigonocarpus Parkinsoni 

 are, almost without exception, associated with the 

 leaflets, petioles, and other organs of Medullosa anglica, 

 while the casts very generally occur together with the 

 Alethopteris foliage, which no doubt belonged to that 

 plant and allied species of Medullosa. Histologically 

 there is a striking agreement in the tracheides, a 

 peculiar, finely scalariform type being characteristic both 

 of the Medullosa and the Trigonocarpus. There is also 

 a certain similarity between the limiting i layers of the 

 sarcotesta and those of the petiole. The evidence is of 

 course far from amounting to proof, but the presumption 

 is entirely in favour of this seed being the fructification 

 of the Alethopteris (probably A. lonchitica), which formed 

 the foliage of Medullosa anglica} 



No pollen-grains have yet been observed in the 

 pollen-chamber of Trigonocarpus, but in another genus 

 of the same group, Stephanospermum, Brongn., recently 

 reinvestigated by Professor F. W. Oliver, they have 

 been found in perfect preservation. The species to 

 which Figs. 173 and 174 refer, Stephanospermum 

 akenioides, Brongn., is one of the numerous seeds, 



1 On Trigonocarpus see Hooker and Binney, "On the Structure of 

 certain Limestone Nodules enclosed in seams of bituminous Coal, with a 

 description of some Trigonocarpons contained in them," Phil. Trans. 

 Royal Soc. vol. cxlv. 1855. Williamson, " On the Organisation of the 

 Fossil Plants of the Coal-measures," Partviii. ibid. vol. clxvii. 1S77. Scott 

 and Maslen, "The Structure of Trigonocarpus" Ann. of Bot. vol. xxi. 

 1907. 



