176 GYMNOSPERJLK. 



Group GYMNOSPERM^. 



Class CYCADALES. 



The term Cycadales is used as a comprehensive designation to 

 include certain fossil genera which are usually spoken of as- 

 Cycads, but do not conform to the accepted definition of the 

 existing Cycadacese. It is well known that the Mesozoic Period 

 was characterized botanically by the abundance of plants bearing 

 pinnate fronds very similar to those of recent Cycads. These 

 extinct types, at least in some cases, have been shown to differ 

 essentially from the modern Cycadacese in their reproductive 

 structures, which diverge too widely from the type represented 

 by the flowers of living Cycads to admit of the inclusion of the 

 fossil genera in the family Cycadacea?. It has been found 

 convenient, therefore, to make use of the class-name Cycadales 

 to include both the existing Cycadaceae and certain fossil genera 

 of which the floral structures are known, with others with which 

 we are acquainted only as regards their leaves or stems. 



Amongst the Jurassic Cycadean genera we have the type 

 Williamsonia, which is of special interest as representing an 

 extinct division of the Cycadales definitely marked off from the true 

 Cycads by the morphology of the floral organs ; this division is 

 spoken of as the Bennettiteas. Other Cycadean genera abundantly 

 represented in the Jurassic flora cannot at present be referred 

 with certainty either to the Bennettitea? or to the Cycadacea?; 

 these may be dealt with as types of Cycadales, without being 

 included in either of the two families or divisions. It is probable 

 that the genus Anomozamites * should be included with Williamsonia 

 as a member of the Bcnnettitese. 



Nathorst (88). 



