465 



CHAPTER LIL 



FLORAS OF THE SECONDARY AND TERTIARY 

 PERIODS. 



Triassic Plants. — With tlie 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 (lig. 713). The trunk is 



713.— Zamia spiralis, a living Cycad. Australia, 



unbranched, often shortened, and bearing a crown of pinnate 

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

 unroll 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 

 natives of warm countries, occurring in South America, the 



VOL. II. 2 a 



