XXXVI] 



CYCADBOIDEA 



391 



The presence of fertile shoots, presumably axillary, is one of 

 the most striking features of Bennettitean stems. The branching 

 is monopodial and not sympodial as in most recent Cycads. The 

 nearest approach to the method of branching in Cycadeoidea is 

 afiorded by some stems of Macrozamia recently described by 

 Chamberlaia^- It is not improbable that some of the flowering 

 branches of Cycadeoidea were branched. Solms-Laubach^ states 

 that he observed certain characters in the secondary axes of 

 Cycadeoidea Gibsoniana which led him to suspect that there may 

 have been fascicled systems of fertile shoots emerging in a body 

 or in close proximity to one another between the leaf-bases of the 

 stem. An example of a branched flowering shoot is described in 

 Williamsonia scotica^, A fertile shoot agrees in structure with 

 the main axis and Scott* states 

 that the phloem is particularly 

 well developed, a feature by no 

 means unusual in fertile branches. 

 These lateral shoots (fig. 514) bear 

 numerous linear bracts each with 

 three collateral vascular bundles, 

 and groimd-tissue composed of 

 thick-walled cells characterised 

 by scalariform pitting (fig. 520) : 

 secretory sacs are abundant. The 

 hypodermal stereome is especially 



developed on the inner face of the bracts. The apex of a 

 lateral shoot has the form of a rounded cushion (figs. 514; 

 521, A, C) similar to the receptacle of many Composites, and on 

 this are borne the sporophylls. It is characteristic of Cycadeoidea 

 that the flowers project very sUghtly beyond the surface of the 

 stem and the peduncles are not exposed except in tangential 

 sections through the leaf-base armour (fig. 517, C, 1, 2). On 

 the fall of the flower or ripe 'fruit,' which is effected by an absciss- 

 layer (figs. 521, C, a; 522, a), a cup-hke scar is left on the stem 

 (c/. fig. 534). This method of flower-production suggests com- 

 parison, mutatis mutandis, with the phenomenon of cauhflory in 



"■ ■ ■ '■ lUHKbkJ " - ' ' 



Fig. 520. Cycadeoidea Gibsoniana. 

 Ground-tissue of bract. (British 

 Museum. 41388.) 



1 Chamberlain (13). See Chapter xxvin., page 6. 



2 Solms-Laubach (91). ' See page 449. " Scott (09) B, 



571. 



