THE PTERIDOPHYTE DIVISION 549 
closely akin to those which do, have more or less hysterophytic 
nurse-plants. 
In endeavoring to trace the evolution of fernworts we con- 
tinually encounter the question as to whether a given type 
or organ of relatively simple form is best regarded as primi- 
tive or degenerate. The evidence available is often conflict- 
ing and has led different botanists to very diverse conclu- 
sions regarding the kinship and evolution of the different 
groups. Another stumbling block has been the difficulty of 
distinguishing between the resemblances that arise from 
similar adaptation to the same environment though in 
different lines of descent, and those resemblances which are 
due to inheritance even under different environments. It 
is now generally admitted, however, that the fernworts of 
the coal period attained much higher development than any 
which have survived, and that several important features, 
such as the development of macrospores, have evolved in- 
dependently in each of the three classes. We have thus 
good reason to suppose that the progressive evolution of 
the Pteridophyta was mainly accomplished in’ geological 
ages long past, that this progress took place along the three 
main lines represented by our modern ferns, scouring-rushes, 
and lycopods, and that these fernworts of to-day are the 
more or less degenerate descendants of giant plants like those 
preserved in coal. 
When we take the adder-tongue fern as possibly represent- 
ing the sort of plant which first evolved from a liverwort 
like Anthoceros, we must accordingly make allowance for 
considerable modification of detail due to special adaptations 
in the course of ages and to more or less degeneration. We 
cannot say much more than that our supposed ancestor of 
the ferns presumably had rows of large sporangia along the 
edges of the blade-like expansion of a growing axis which 
put forth, below, cylindrical projections for absorbing water. 
‘From such an ancestor, ferns, scouring-rushes, and club- 
mosses may perhaps be supposed to have evolved, one or 
another according as the stem-parts or leaf-parts reached 
greater or less, or about equal development, and the spore- 
sacs were multiplied or reduced in number and diminished 
