5] EVOLUTIONARY DEVELOPMENT AND PAST HISTORY 141 



Fig. 34. — A reconstructed Cycadeoid and parts of living and fossil Ginkgoales. 



A, Cycadeoidea, showing the tiower-like strobili on the squat stem ( ■; about "iV); 



B, branch of Ginkgo with seeds ( ,< f ) ; C, leaves of two species of Baiera, Mesozoic 



Ginkgoales ( < about §). 



Mesozoic, when its members were far more (probably very) wide- 

 spread. 



Of comparable antiquity, extensive development in the IXIesozoic, 

 and bare persistence to the present day are the Ginkgoales, repre- 

 sented among living types by only the Maidenhair-tree, Ginkgo 

 hiloba. This is very restricted in anything like a wild state, but 

 is widely familiar in cultivation ; a female sprig is shown in Fig. 34, B, 

 as also are leaves of relatives which were almost world-wide in the 

 Mesozoic. Like the Cycads, Ginkgo has motile sperms ; its obviously 

 primitive characters have led to its being called a ' living fossil '. 



An earlier, long-extinct and apparently quite distinct group of 

 Gymnosperms, the Cordaitales, flourished chiefly in the later part 

 of the Palaeozoic, constituting with the Pteridosperms the bulk of 

 the seed-plants of the Carboniferous coal-forests. Their origin 

 is obscure, the earliest known members apparently being already far 

 advanced. The Cordaitales were mostlv large trees with sizeable 

 flattened leaves and bearing their pollen and seeds in slender strobili 

 as indicated in Fig. 35. 



The other major group of fossil Gymnosperms is the Conifers, 

 whose surviving representatives afford the vast majority of living 

 Gymnosperms. Examples of Conifers are illustrated in Fig. 18, 

 their general features being described in Chapter II. They bear 

 some resemblance to Cordaitales, and as fossils went back at least to 

 the upper Carboniferous, an example from that time being shown 

 in Fig. 36, A. Subsequently they appeared to reach their develop- 

 mental climax in the Mesozoic, when several were similar in external 

 form to those surviving today. Before the end of that era they began 



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