Zoe 
leaves are shown somewhat exaggerated as to size, so that their 
much divided fan-lke form can be clearly seen, 
Baiera, which is known almost entirely from impressions of the 
foliage, is generally considered an early member of the order 
‘Ginkgoales) to which the Ginkgo belongs. It makes its appear- 
ance in the Permian, becomes especially abundant during the older 
Mesozoic, and some stragglers survive as late as the Cretaceous. 
During this long time Baiera attains a world wide distribution and 
has been found on all the continents. Since many of the features 
of this order can only be surmised from the features of the single 
existing species of Ginkgo (Ginkgo biloba), this should be kept 
in mind in all attempts to relate these plants to the Cordaites plexus 
on the one hand and to the modern conifers on the other. 
8. Mesozoic Gymnosperms 
The transparency devoted to Mesozoic Gymnosperms shows 
four highly characteristic Mesozoic types. The Araucarioxylon 
night well be an actual photograph taken of a modern Araucaria 
grove in southern Brazil or in the Chilean Andes. The modern 
species are about fifteen in number in two genera, and are con- 
fined to the Australasian and South American regions. They 
have many features of cone structure and trunk anatomy which 
serve to set them apart from all other existing conifers, and their 
true position among the Gymnosperms is a subject about which 
there is much difference of opinion. 
Their remote ancestry is also one of dispute since the anatomy 
of the secondary wood is not appreciably different from that of 
Cordaites, and the term Araucarioxylon has been often used with 
such a dual meaning. As has been already mentioned, Walchia, 
which is shown among the Paleozoic Gymnosperms, has many 
Features which suggest that it may have been an ancient member 
of the Araucarian line. The occurrence of large cones, single- 
seeded cone scales, and impressions of foliage in rocks of the early 
Mesozoic give indubitable evidence of the presence of Araucaria- 
like trees. These types become cosmopolitan during the Triassic 
and Cretaceous, and shrink to their present range at the antipodes 
during the Tertiary. 
The other three Mesozoic Gymnosperms shown belong to a 
