228 EVOLUTION OF PLANTS 
their own in modern times better than any other Coni- 
fers. At present, these are decidedly the prevailing 
types of coniferous trees, but even these, in most re- 
gions, show signs of yielding to the encroachment of 
the angiospermous trees. 
While various fossils from the Carboniferous and early 
Mesozoic formations have been assigned to the Angio- 
sperms, it is not until the later Cretaceous is reached 
that undoubted remains of these plants occur. Here 
are found unmistakable traces of both Monocotyledons 
and Dicotyledons, but most of the earliest remains are 
of such character as to throw little light upon the 
relation which these two groups bear to one another. 
Among the earliest forms of which recognizable re- 
mains are found, are palms and screw-pines among 
the Monocotyledons, and birches, willows, and poplars 
among the Dicotyledons. It need not necessarily follow 
that these are the most primitive of the Angiosperms, 
although they are doubtless among the more primitive 
types. Their preservation is simply due to the fact 
that their tissues were firm and resisted decay long 
enough to leave clear impressions. Most of the living 
Angiosperms which are considered as probably the most 
primitive, especially among the Monocotyledons, have 
extremely delicate and perishable tissues, which, as in 
the case of alge, could hardly be expected to leave 
recognizable fossil remains. 
In the later Tertiary rocks, remains of Angiosperms 
became very abundant, and most of the existing groups, 
especially of Dicotyledons, can be distinguished. It is 
evident that at last a type of plants has been evolved 
which is rapidly crowding out the less perfect types 
