496 PAL^OBOTANY. 



belong in part to Carboniferous genera. A characteristic 

 genus, however, is Walchia (fig. 391), distinguished by its lax 

 short leaves. This genus, though not exclusively Permian, is 

 mainly so, the best-known species being the W. piniformis. 

 Here, also, we meet with Conifers which produce true cones, 

 and which differ, therefore, in an important respect from the 

 Taxoid Conifers of the Coal-measures. One of the most 

 characteristic of these is the Ullmania selaginoides, which oc- 

 curs in the Magnesian Limestone of Durham, the Middle 

 Permian of Westmorland, and the " Kupfer-schiefer " of 

 Germany. 



CHAPTER XLVI. 



FLORAS OF THE SECONDARY AND TERTIARY 



PERIODS. 



TRIASSIC PLANTS. With the Trias we commence what has 

 been aptly termed the "Age of Cycads," from the predomi- 

 nance of the plants of this group in the Mesozoic vegetation. 

 The Cycads are a group of Gymnospermous Exogens, the 

 form and habit of growth of which present considerable re- 

 semblance to those of young Palms (fig. 392). The trunk is 



Fig. 392. Zaniia spiralis, a living Cycad. Australia. 



unbranched, often shortened, and bearing a crown of pinnate 

 fronds. The leaves are usually " circinate " that is, they un- 

 roll in expanding, like the fronds of Ferns. The ovules are 

 borne upon the edge of altered leaves, or are carried on the 

 scales of a cone. All the existing species of Cycads are 



