XXXVI] CYCADEOIDEA 379 



differing in the habit of the fertile shoots (fig. 542), and there 

 is evidence that similar stems bore Ptilophyllum and Dictyozamites 

 fronds 1 ; but only unexpanded leaves have been found in actual 

 connexion with Cycadeoidea stems. Wieland 2 discovered young 

 pinnate fronds, agreeing in the form of the pinnae with Zamites 

 and with some forms of Encephalartos, embedded in a thick mass 

 of ramental scales in the terminal bud of a stem: the rachises 

 were erect and the two-ranked pinnae imbricate and folded 

 inwards (fig. 512), the vernation being like that of Dioon and not 

 circinate as in Cycas and Ferns. The mesophyll of the leathery 

 pinnae is differentiated into palisade and lacunar parenchyma, 

 and the bundles are said to be 'mesarch' though on this point 

 more information is desirable. Each bundle is surrounded by 

 a sheath of thick-walled cells and the same tissue forms I-shaped 

 girders as in similar recent leaves. In one species, Cycadella 

 ramentosa 3 , the rachis of a young frond found among the leaf- 

 bases had a broad U-shaped vascular strand. 



In most Cycadeoidea stems a characteristic feature is the 

 occurrence of reduced leaves, or bracts, arranged spirally about 

 a cone which sometimes projects slightly beyond the general level 

 of the persistent leaf-bases, or the cones may be fully developed 

 yet still more or less hidden within the armour of petiole-bases 

 (fig. 517, C). These cones, or flowers, are borne at the apex of 

 lateral axillary shoots, and it is characteristic of the genus that 

 they never project more than a very short distance beyond the 

 truncate stumps of the old leaf -bases. The axis of a flowering 

 branch bears numerous linear, hairy, bracts (figs. 513; 514, b) 

 which with their thick felt of ramenta constitute an efficient 

 protective investment. The summit of a fertile shoot forms a 

 rounded hemispherical cushion (fig. 514), or the receptacle may 

 be more elongate and conical (fig. 513) and in some species pyri- 

 form 4 . The flowers are generally bisporangiate, but the fact 

 that in flowers with mature microsporophylls the ovules are small 

 and apparently immature (fig. 513) makes it difficult to determine 

 whether the megasporophylls are merely immature or functionless 

 as in the male flower of Welwitschia (cf. fig. 818). It would 



1 See page 489. 2 Wieland (99); (06) p. 87. 



3 Wieland in Ward (05) B. p. 200, PI. Lxm. 4 Wieland (14). 



