462 SCIENCE PROGRESS. 



Among Wealden ferns, which may be referred to as 

 probable representatives of definite families or genera, the 

 following may be mentioned : — 



Ruffordia Gopperti (Dunk.) * (? Schizaceae), species of 

 Acrostichopteris' 1 {cf. Acrostichuni), also species referred to 

 Adiantiim? Aspidiimi 2 and other genera. 



Gymnosperm/E. — i. Cycadales. The abundance of pin- 

 nate fronds of different species of " Cycads " is a charac- 

 teristic feature of both Wealden and Jurassic rocks. In 

 endeavouring to determine fossil cycadean leaves, we have 

 to bear in mind the fact that it is practically impossible in 

 many cases to be certain whether the fronds were borne by 

 the stems of true Cycads or by stems of the genus Bennettites, 

 which belongs to another division of the Cycadales. The 

 Bennettiteae represent an extinct group of plants which 

 flourished during the Jurassic and Lower Cretaceous epochs ; 

 in certain respects they agree very closely with the recent 

 Cycadeae, which are represented by Cycas, Zamia, Dioon, 

 Encephalartos, and a few other genera practically confined 

 to tropical regions. The stems of Cycads — or " Sago 

 Palms," as they are sometimes popularly called — and of the 

 Bennettiteae resemble one another in general appearance, but 

 the nature of the reproductive organs in the latter family 

 precludes their inclusion among the true Cycads. In the 

 Cycads the male and female flowers are borne at the apex 

 of the trunk, and with the exception of the female flowers 

 of the genus Cycas, they have the form of cones consisting 

 of crowded sporophylls ; in the Bennettiteae, on the other 

 hand, there are special branches given off at right angles to 

 the main stem, which terminate in an inflorescence of a 

 more complex and highly differentiated type than the flowers 

 of the Cycads. The existence of these fertile lateral shoots 

 forms a ready means of distinguishing a Bennettitean from 

 a Cycadean stem ; the stem of Bennettites is enclosed in an 

 "armour" of persistent leaf-bases as in the ordinary Cycad, 

 but there are crowded series of smaller scale-leaves here 

 and there in the axil of a petiole, which mark the position 



1 Seward (i), p. 76 ; pis. iv.-vi. 2 Fontaine, pis. clxxi. and clxxii. 

 3 Saporta, pis. x., xviii., xxix., etc. 



