FKRNS AND FKRN ARIylKS. 147 
“small ferns lit 
Their teeth to the polished block” 
and not only can they grow in all these diverse environ¬ 
ments, they can also hold their own against th'e encroach¬ 
ments of more highly organized plants. Finally, while 
their ancient cousins are restricted almost entirely to cool 
or temperate regions, they thrive nearly from pole to pole, 
and reach their finest development in sub¬ 
tropical and tropical regions. Witness 
Bermuda, with not less than four hundred 
species,some of them comprising the great 
tree-ferns forty or more feet high and with 
a stem, botanically a “caudex,” simulating 
the trunk of a good sized tree. 
It is specialization, then, which has en¬ 
abled modern ferns to hold their own so ex¬ 
tensively. against the encroachments of the 
seed-bearing plants. Before entering into 
the study of the Polypodiacese, as a family, 
it may be well to consider the relation of 
specialization to evolution in general. Spe¬ 
cialization is the development of a certain 
plant form along certain well defined lines, 
for the accomplishment of certain ends. It 
is therefore only one phase of evolution. If 
evolution be represented diagrammatically 
by a line ascending from left to right, spe¬ 
cialization may be represented by a horizon¬ 
tal line from left to right. So if we choose 
to represent the whole progress of evolution 
in the plant world, by such an ascending 
line, the various specializations which have arisen will be 
represented by as many horizontal lines striking off from 
that line. The idea I wish to convey is, that specialization 
is a check to general evolution in the class of plants in 
which it has taken place. Therefore it follows that not the 
PTg. 2 . 
