INTERPRETATION OF FOSSIL PLANTS 
11 
meaning of their fossil representatives. Such a genus is Ficus; 
and many others might be mentioned. Fossil representatives of 
such genera may have some value when they are associated with 
other types whose evidence is consistent. Some botanists are ac¬ 
customed to ridicule the possibility of identifying plants from 
their foliar remains, and a favorite method of their criticism is 
to point out the similarity in appearance of unrelated forms. A 
good illustration of this point of view is given by Seward in vol¬ 
ume one of his text on Fossil Plants where he figures specimens 
of the genera Restio, Equisetum, Casuarina, Ephedra and Poly¬ 
gonum, and he might have added several others, the implication 
being that the paleobotanist is likely to have to distinguish between 
these. A cardinal principle in the identification of leaves is that 
the fossils will occur in a normal ecological grouping. Kaulfus- 
sia leaves will never be associated with those of horse chestnuts 
(^sculus), humid tropical types will never be associated with 
arid or cold temperate types, nor will present day Australian 
types be in association with north temperate, or African types be 
mixed with Alaskan types. Coastal types will not normally be 
mixed with montane types, if the physical conditions bring about 
such an admixture, the incompleteness of the latter element or the 
genera represented will give a clue to the fact of mixing. 
Except in Pleistocene floras herbaceous plants are of less signi¬ 
ficance than arborescent. Aquatic forms, although clearly indi¬ 
cative of habitat are of less importance than terrestrial forms in 
all questions of climate, since they are generally much more widely 
distributed, and less responsive to environmental changes. 
Land-derived vegetable material may drift long distances sea¬ 
ward from the mouths of great rivers like the Amazon, or the 
Orinoco, and many instances of this sort may be found in the 
Challenger and other oceanographic reports: or buoyant fruits, 
specialized for distribution by ocean currents, may frequently 
cross the ocean basins. Specific examples, such as Nipa palms, 
sea-beans, and Saccoglottis, may be cited. Such fruits will be 
post-Mesozoic in age, or at least will not be present in beds older 
than Late Cretacic time. Those mentioned, and in fact the ma¬ 
jority of drift fruits of any size originate exclusively in tropical 
and sub-tropical environments at the present time. If such occur 
as fossils in high latitudes, as in the Pleistocene of Norway, or in 
