CYCADOFILICALES AND CYCADALES 



301 



lem. After a narrow parenchymatous interval the pitted elements 

 of the centrifugal metaxylem are seen in close proximity to the 

 phloem. The general situation in the transverse and longitudinal 

 sections of the foliar strands shown in the two figures is universal 

 for the Cycadales, any minor divergences which have been ob- 

 served being mainly the result of the smaller size of the strands in 

 the genera other than Cycas. 



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FIG. 214. Longitudinal section of a foliar strand in Cycas revoluta 



The foliar traces in the genus under consideration show other 

 interesting features of organization in the lower part of their 

 course, where they pass from the base of the petiole of the leaf 

 into the cortex of the axis. These features have to do both with 

 the arrangement of the traces and with their anatomical organiza- 

 tion. In the vegetative axes of living genera of the Cycadales 

 the foliar strands, instead of passing directly outward to their 

 respective leaves, pursue a meandering course through the cortex 

 and are known as "girdles." This condition is confined to the 

 modern genera, for in the Mesozoic representatives of the group 

 united under the caption of Bennettitales the leaf traces pass 

 directly to their corresponding leaves. Interestingly enough this 



