316 PLANT MORPHOLOGY 



like leaves at the summit. The stems were covered with an armor of 

 persistent leaf bases and a mass of woolly scales, forming a ramentum, as 

 in many tree ferns. The stems of WiUiamsoniella and Wielandiella were 

 slender, dichotomously branched, and smooth, with a cluster of leaves at 

 the points of forking. Except in WiUiamsoniella, the leaves of the 

 Bennettitales were pinnately divided into many leaflets. 



Fig. 264. Cycadeoidea ingens. Photograph of a model of the strobilus in the Chicago 

 Natural History Museum. 



The stem was an ectophloic siphonostele, a cross section showing a 

 large pith, a thin vascular cylinder, and a thick cortex. The vascular 

 bundles were collateral and endarch. Secondary wood, although scanty 

 in amount, was always present. Most of the tracheids were scalariform, 

 but in some cases were pitted. The leaf traces were single and direct, 

 becoming mesarch after entering the leaves. 



Strobilus. In Cycadeoidea numerous strobili were borne on short stalks 

 occurring among the leaf bases, each strobilus being axillary (Fig. 263). 

 In Williamsonia the cones were long-stalked and borne in the apical crown 

 of leaves. In the two other genera the strobili were borne singly in an 

 upright position where the stem underwent forking. The order is charac- 

 terized by bisporangiate strobili (mostly monosporangiate in William- 



