396 BENNETTITALES [CH. 



it is constructed on essentially the same plan as the flowers of 

 Cycadeoidea (Bennettites) Gibsoniana, and in both cases there is 

 no indication of the presence of microsporophylls. The type- 

 specimen is 5-5 cm. long and 3-5 cm. broad, ovoid, and charac- 

 terised by a depressed cushion-like receptacle as in Cycadeoidea 

 Gibsoniana. The enveloping bracts with their ramental scales 

 agree generally in structure with those of the English species 

 and, except as regards the ramenta, with Williamsonia scotica: 

 numerous stomata occur on the lower surface; the ground-tissue 

 consists of thick-walled parenchyma and the narrow pit-canals 

 simulate the scalariform bands in Cycadeoidea Gibsoniana (cf. 

 fig. 520). The pitted sclerous cells in the bracts of W . scotica are 

 of the same type. There is an anastomosing system of secretory 

 canals, also several vascular bundles like those in C. Gibsoniana 

 but more numerous; the latter are composed of a group of 

 phloem-elements abutting externally on fibres, a well-defined 

 cambium, and radially disposed scalariform tracheids: internal 

 to the protoxylem is a group of elements considered by Lignier 

 to be centripetal xylem. From the branching and slightly 

 divergent course of the bundles in the upper part of the bracts 

 Lignier concluded that these organs represent the basal portions 

 of leaves originally provided with a terminal limb. It may be 

 that the small lateral appendages to some of the bracts of William- 

 sonia scotica (fig. 561, 1) afford support to this view. 



Megasporophylls (seed-stalks and seeds). These organs, 

 3 4-5 cm. long and approximately 1-5 mm. in diameter, are in 

 most cases imperfectly preserved. In transverse section and at a 

 level of 1 cm. above the receptacle a stalk bearing an atrophied 

 seed shows the following features : an epidermis with very thick 

 internal walls encloses a parenchymatous ground-tissue with an 

 axial conducting strand. At a higher level the epidermal cells 

 have walls of uniform thickness, and a hypodermal layer of cells 

 with coloured contents is differentiated from the ground-tissue (fig. 

 524, D, ac). As the seed-base is approached the epidermal cells 

 tend to separate from one another and divide longitudinally, 

 the compact epidermal layer being replaced by an envelope of 

 tubular, dissociated, cells (fig. 524, D, Et). Similar tubular 

 elements occur in the seed-stalks of Cycadeoidea Gibsoniana. 



