XXXV] MITROSPERMUM 345 



passes through the sclerotesta, e, e' , fig. 501, E, before giving 

 off two bundles which bend back ('faisceaux recurrents'), traverse 

 the shell, and then pass up the sarcotesta in correspondence with 

 the feebly developed lateral keels as far as the micropyle, while 

 in Cardiocarpus (fig. 500, B) the bundles are given off before the 

 main strand reaches the sclerotesta. Similar recurrent bundles 

 occur also in Mitrospermum (fig. 494, K) 1 . 



Mitrospermum. A. Arber. 



Mitrospermum compressum (Williamson). Mrs Arber 2 pro- 

 posed the name Mitrospermum 3 , suggested by the peculiar form 

 of the seed-base, as a substitute for Cardiocarpon for Williamson's 

 species C. compressum* from the Lower Coal Measures of Lanca- 

 shire. The seed is platyspermic and there is some evidence that 

 it split into two valves along the principal plane (the longer 

 axis of the section, fig. 494, L). The diagrammatic and partially 

 restored longitudinal section reproduced in fig. 494, K, shows 

 the main features : a sarcotesta, sa, covers the surface of the testa 

 as a thin layer except at the edges of the flattened sides where it 

 forms a wing-like border; preserved as an impression the seed 

 would be assigned to Samaropsis. The sclerotesta, sc, has a 

 pointed apex which surrounds the lower third of the micropyle 

 and a broad base perforated by the chalazal vascular strand. 

 There was probably a narrow inner flesh as in Trigonocarpus and 

 recent Cycadean seeds (fig. 494, K, cf). The nucellus was free 

 from the integument except at the base, as in Trigonocarpus and 

 Stephanospermum (fig. 494, K, n) : internal to the shrivelled 

 remains of the inner flesh there was a nucellar tapetum surrounding 

 the megaspore. Details as to the pollen-chamber are lacking 

 though there are indications that it resembled that of some 

 species of Cordaitean seeds. The main vascular supply passes 

 through the sclerotesta and then forms a low cushion of short 

 reticulate elements below the base of the nucellus from which 

 two bundles are given off (fig. 494, K, v) in the principal plane. 

 The course of the bundles which pierce the sclerotesta led Mrs 

 Arber to remove this seed from Cardiocarpus, as recently defined 

 by Bertrand 5 , since in that genus the integumental bundles have 



1 See page 314. 2 Arber, A. (10). 3 fj.lrpa, a Persian cap. 



4 Williamson (77) B. p. 257, Pis. xv. xvi. 6 Bertrand, C. E. (08 2 ). 



