414 



BENNETTITALES 



[CH. 



no evidence of the presence of any reproductive organs. A similar 

 bud is described by Lignier^ in the stem of C. micromyela. The 

 absence of lateral flowers is, however, hardly a sufficient reason 

 for separating this stem generically from other species of Cyca- 

 deoidea: negative evidence in this case is of doubtful value. 

 While it is possible that the strobih were terminal as in most 

 recent Cycads, it is more probable that they were lateral. The 

 surface-features, though not perfect, are for the most part 

 sufficiently well preserved to enable one to recognise the bract- 

 encircled axes of strobih were any present. If as Wieland beUeves, 

 and he is probably correct, the production of flowers was the 

 culminating event in the hfe of these Cycadean plants, the absence 

 of fertile shoots is merely an expression of immaturity. It is, 



Fig. 5.37. Cycadeoidea gigantea. Transverse section of the stem. 



however, difficult to understand how lateral branches could find 

 their way to the surface among the crowded and cork-covered 

 leaf-bases of the stem. The absence of flowers may be due to 

 some \infavourable external conditions. The petioles consist of 

 parenchymatous ground-tissue with many secretory sacs and in 

 some cases twelve partially preserved vascular bundles: the 

 xylem consists of radial rows of centrifugal tracheids and medul- 

 lary rays, but it is not possible to say whether any centripetal 

 xylem was present. A fairly thick band of phelloderm and 

 periderm, apparently subepidermal in origin, forms the peripheral 

 tissue, and in places epidermal cells with attached ramenta are 

 clearly preserved. The ramenta are of the type characteristic 

 of the majority of fossil Cycadean stems. Stomata were found 

 showing a pair of guard-cells and apparently two subsidiary cells : 

 the epidermal cells have straight walls. 



1 Lignier (01). 



