436 G. R. Wieland — American Fossil Cycads. 



nettitese, wholly extinct, and so different as to merit ordinal 

 rank." 



In their leaf structures these two orders are essentially sim- 

 ilar. In trunk structure there is a well-marked minor dif- 

 ference affording a convenient means of separation, — the leaf 

 traces (but not always the peduncle traces) of the Cycadacese 

 arising as secondary cortical bundles, while those of the Bennet- 

 titacese are primary, passing out directly from the xylem zone. 



In fructification the basis of separation rests on the fact that 

 in the Cycadacese the microsporophylls are always organized 

 into a distinct cone, while the macrosporophylls may retain 

 primitive characters as carpellary leaves. In the Bennettitacege 

 the opposite holds true. The microspores are borne on primi- 

 tive pollinial leaves, while the macrospores are organized into 

 an ancient type of cone. 



It may be remarked that the gap between Cycas and the 

 other living cycads is clearly lessened by the analogy afforded 

 by the staminate fronds of the Bennettitacese. The living 

 cycads may hence most conveniently be held as composed of 

 two divisions of equal value, the Cycadese and Zamiese. 



Yale Museum, New Haven, Conn., April 20, 1901. 



