139 
arly Mesozoic times, during the Triassic period, the cycad- 
ously with the first appearance of the higher angiosperm type 
i d by our 
were, ae the dominant type of recent es this 
restricted in their distribution. Climatic and physiographic 
changes r scaled in their limitation or extinction in Arctic and 
ene regions, and ae ee in the Tertiary period, 
they h ad b 
ical regions where n em. There are n 
ative in Europe, and our only native representatives in the 
United States are four species of Za: t occur in Florida 
was a species of Encephalartos—a genus that is now found only 
: Africa, far to the south—and that apparently the last ones 
t survived in North America were species of Diodn, almost 
ndtingcabe from the two remaining living species of the 
genus, now found only in Mexico. 
