628 DAVID WHITE 
the GANGAMOPTERIS flora are indicated in the accompanying table. 
No attempt is therein made to include or show the equivalents of all 
the Mesozoic formations. 
ORIGIN OF THE GANGAMOPTERIS FLORA 
The types composing the GANGAMOPTERIS flora belong, as Pro- 
fessor Arber’ has so well shown, almost exclusively to families already 
well known in the cosmopolitan flora. ‘They constitute genera or 
species more or less closely bound to their northern relatives, though 
often differing much in form and aspect. In general they appear 
simpler in figure, with a tendency to thickness and rugosity of leaf 
that may indicate either a xerophytic or pseudoxerophytic condition. 
On the whole the aspect of the plants distinctly suggests environ- 
mental conditions unfavorable to luxuriant plant growth. That the 
development of this flora was directly consequent to a Permo-Carbon- 
iferous period of regional refrigeration is now no longer questioned. 
In its purest and simplest composition, and with remarkable uniform- 
ity, it is found in India, Austraila, South Africa, and South America 
immediately above apparently contemporaneous formations bearing 
evidence of the work of ice. The conditions which brought the 
new flora into being banished or exterminated the Cosmopolitan or 
northern Permo-Carboniferous flora from the GANGAMOPTERIS 
province. The early return of a few of the hardier Lycopodineous 
forms in Argentina, Brazil, and South Africa, has already been 
mentioned. Most of the former plant population of the province 
died in exile, and only their posterity, especially among the Cladophle- 
boid ferns and the Araucarian, Ginkgoalean and Cycadalean gymno- 
sperms were able to traverse the lost territory and contest the 
GANGAMOPTERIS occupation. 
It is not probable that any serious hindrance other than altitude 
or climate seriously opposed the return of the northern flora to the 
GANGAMOPTERIS province in either the Western or the Eastern Hemis- 
phere. The early return of certain Lepidophytes to the Brazilian 
and South African regions and the invasion of the Russian area by 
some of the older Gondwana elements is evidence of the efficiency of 
t Catalogue of the Foss. Pl. of the Glossopteris Flora in the Department of 
Geology in the British Museum, 1905, Pp. XX. 
