BENNETTITALES 



57 



The megasporangium. — ^The solitary megasporangium is terminal 

 on a slender stalk, which represents the rachis of the sporophyll. In 

 the Cycadales, all the ovules are lateral, while, here, all are terminal 

 (fig. 51). In the two great lines, evolution has taken two distinct 



I 



Fig. si 



Fig. 52 



Fig. 51. — Bennettites gibsonianus: diagram of female strobilus, showing terminal 

 seed with dicotyl embryos. The sporophylls are long and slender, and they alternate 

 with sterile bracts (sporophylls). The whole strobilus is surrounded by bracts. — Modi- 

 fied by ScoTTS''t after Solms-Laubachs'^ and Potonie.''S5 



Fig. 52. — Bennettites morieri: longitudinal section of a seed; a, micropylar tube; b, 

 prismatic layer; c, pulpy tissue; d, "corpuscular" mass; e, interseminal scale;/, embryo 

 space; g, remains of nucellus; h, chalaza; i, tubular envelope; k, micropylar canal; /, nu- 

 cellar beak; m, pollen chamber; n, fibrous stratum; 0, basal expansion of n; p, pedicel 

 bundle. — After Wieland's^*" reproduction of Lignier'sJS9 figure. 



courses. Starting with sporophyll, bearing ovules both laterally and 

 at the apex, the lateral ovules, in the Bennettitales, became sterile 

 and disappeared; while in the Cycadales the top of the sporophyll 

 became sterile and the lateral ones remained. 



