306 G. R. Wieland — American Fossil Cycads. 



A careful examination of the summit of the trunk showed that, 

 as found in the field, it had been subjected to the erosive action 

 of sand-laden winds which had partially exposed several trans- 

 verse sections of the tips of young leaves. It was found that 

 these belonged to a circularly placed series just ready to emerge 

 at a distance of from 5 to 8 cm from the apex. Several pairs of 

 these leaves enveloped in ramentum were removed for study, 

 and the disposition of their parts with reference to the trunk 

 determined from longitudinal, transverse, and tangential 

 sections. 



As so removed, each rachis with its attached pinnules formed 

 an erect subcylindrical, or spindle-shaped, body, 6 cm in 

 length, with a long diameter of 15 mm coinciding with the 

 radius of the trunk, and a short diameter of 12 mm at right 

 angles to it. The rachis was erect and situated distally on the 

 long diameter. It bore the pinnules inclined inwards in two 

 imbricating ranks, formed by the two rows of pinnae on each 

 leaf, in such manner that their upper surfaces all faced towards 

 the axis of the trunk. 



A clearer perception of the arrangement of the pinnules 

 with respect to the rachis and the trunk may be had if an 

 ordinary, expanded, young Zamia leaf is considered in its 

 natural position on the summit of the trunk. If the pinnules 

 of such a leaf are folded toward the axis of the trunk in two 

 ranks, and these ranks are brought together side by side, the 

 position of the parts in the unexpanded young leaf of Cycade- 

 oidea will be paralleled. As just stated, it at once becomes 

 apparent that the rachis is farthest away from the trunk, and 

 that the upper side of each pinnule faces the axis of the trunk. 

 This is also the relative position of the parts in the unexpanded 

 young leaf of Zamia. Cycadeoidea thus had the direct mode 

 of prefoliation characterizing the existing North American 

 cycads Zamia and Dioon. 



The Cycadeoidean Leaf Structure. 



While an exhaustive treatment of the anatomy of these 

 leaves must be deferred for the present, the features of more 

 immediate interest may be here described. 



The exact arrangement of the pinnules and of their fibro- 

 vascular bundles is shown in the transverse section, figure 2 

 (Plate YII), and in the longitudinal section, figure 3, the 

 general position of these sections being indicated in figure 1. 



The transverse section, figure 2, shows that, just above the 

 termination of the rachis, there are 20 pairs of projecting pin- 

 nules. Since the pinnules nearest the rachis must necessarily 



