"746 EEIGN OF THE GYMNOSPEEMS. 



The reign of the Gymnospermous Dicotyledons is divided into two 

 periods : the first, in which the Coniferse predominate, while the 

 Cycadacess scarcely appear ; the second, in which the latter family 

 preponderates as regards the number of species, and the frequency and 

 variety of generic forms. Cycadaceae (figs. 925, 926) occupied a more 

 important place in the ancient than in the present vegetable world. 

 They extend more or less from the Triassic formation up to the 



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Pig. 925. 



Tertiary. They are rare in the Grfesbigarr^ or lower strata of the 

 Triassic system. They attain their maximum in the Lias and 

 Oolite, in the latter of which 60 species have been enumerated, and 

 they disappear in the Tertiary formations. Schimper thinks that 

 Trigonocarpum (15 species), Ehabdocarpum (24 species), Cardiocarpum 

 (21 species), Carpolithes (9 species), and Oycadinocarpus (6 species), 

 are aU fruits of Cycadeae. Many supposed fossil Oycads are probably 

 Conifers. It is important to notice that in an existing Oycad called 

 Stangeria paradoxa the vernation of the leaf-divisions is involute and 

 inflexed, and the veins of the pinnse rise from a true midrib and fork, 

 characters which are more commonly met with in Ferns. 



In Brongniart's Vosgesian period, the Grfesbigarrd, or the Eed 

 Sandstones and Conglomerates of the Triassic system, there is a change 



Fig. 925. Cycas revoluta, one of the species of Cycas of the present flora of the glohe, 

 with its scale-like stem and pinnate fronds. Fig. 926. Encephalartos (Zamia) pungens, 

 one of the Cycadaceje at present existing on the globe. 



