PAST HISTORIES OF PLANT FAMILIES 



lOI 



Fig. 69. — Leaf Impression 

 of Ginkgo from Mesozoic 

 Rocks of Scotland 



but probably they are closely allied. Fig. 69 shows a 

 typical impression from the Lower Mesozoic rocks. In 

 this specimen, the cells of the epidermis were fortunately 

 sufficiently well preserved to be seen with the microscope, 

 and there is a distinct difference in 

 the size and shape of the cells of 

 living and fossil species, see fig. 70; 

 but this difference is slight as com- 

 pared with the great similarity of 

 form and appearance, as can be seen 

 on comparing figs. 69 and 66, b, so 

 that the fossil is at the most a dif- 

 ferent species of the genus Ginkgo. 

 Among the fossil leaves there is 

 greater variety than among the 

 living ones, and some which are very 

 deeply lobed so as to form a divided 

 palm-like leaf go by different names, e.g. Baiera, but 

 they are supposed to belong to the same family. Fossil 

 seeds and male cones are also known as impressions, 

 and are found far back in the 

 Mesozoic rocks. From the 

 fossil impressions it is certain 

 that Ginkgo and plants closely 

 allied to it were verv wide- 

 spread in the past, as they are 

 found all over Europe as well 

 ■as the other continents. Par- 

 ticularly in the Lower Meso- 

 .zoic rocks Ginkgo seems to 

 have been a world-wide type 

 growing in great abundance. 

 In the Palaeozoic the 

 records are not so undoubted, 

 but there is strong evidence 



which leads us to suppose that if the genus now living 

 were not then extant, at least other closely related 

 genera were, and there seems to be good grounds for 



Fig. 7c. — Showing Epidermis witli 

 Stomates from tlie lower side of the 

 Leaf seen in fig. 6g 



e, Epidermis cells; s, stomates; v, 

 long cells of epidermis lying over the 

 veins. 



