FEBRUARY 1, 1901.] 
scribed as having characters intermediate 
between those of the ferns and the Gymno- 
sperms, and he thus opened the way for the 
final recognition of the Cycadofilices by 
Potonié, to which also such hitherto doubt-: 
ful types as Medullosa and Myelopteris 
undoubtedly belong—a group of plants the 
recognition of which has gone far toward 
clearing up most important questions re- 
lating to the phylogeny of the Gymno- 
sperms, and of the Cycads in particular. 
It will thus be seen that toa large extent 
at least the study of fossil plants has pro- 
ceeded on lines parallel with those in other 
branches of botanical science, and that the 
growth of the subject has substantially 
been directed by men eminent as botanists. 
Originally employed asa distinctive term for 
a subject supposedly outside of botanical sci- 
ence, paleobotany has more recently come 
to have equal rank with other divisions of 
the science such as histology, physiology, 
ecology, ete. Such artificial distinctions 
as formerly existed are fast disappearing, 
and we are now rapidly approaching, if we 
have not already entered upon, the first 
_ stages in the realization of that harmony 
between the botany of recent and extinct 
forms, the accomplishment of which Ward 
in 1885 recognized as so eminently desi- 
rable, but considered so difficult of attain- 
ment. 
One of the earliest views attaching to the 
relations of paleobotany and geology was 
that of the supposed value of fossil plants 
in determining the age of deposits, and 
this found expression in the idea that the 
sequence with which plants were known to 
occur must be correlated with the succes- 
sion of geological formations in such a way 
that the age of the latter could be ascer- 
tained by an examination of the flora. Al- 
though fundamentally correct, the precise 
application of the principle was found to 
lead to such erroneous conclusions that 
geologists soon came to look upon the evi- 
SCIENCE. 
165 
dence of fossil plants as untrustworthy, and 
itis only within recent years that there has 
been any material alteration in this point 
of view. So long ago as 1871, however, 
we find Sir William Dawson,'who possessed 
a deeper insight into the bearings of evi- 
dence derived from fossil plants than was 
the case with the majority of geologists, 
expressing the opinion that “ fossil plants 
have hitherto been regarded as of much 
less importance than fossil animals in de- 
termining the age of rocks, ;and in some 
portions of the geological series, where for- 
mations are strictly marine, their value is, 
no doubt, quite subordinate. But there are 
portions of the geological formations * * * 
in which their value becomes much greater’’; 
and in 1892 we find him giving a more pro- 
nounced expression of opinion when he says 
that ‘‘The history of geological discovery 
in the Canadian Northwest affords a con- 
vineing proof of the value of fossil plants 
when carefully collected, * * * in deter- 
mining the geological ages of the forma- 
tions in which they occur, while there can 
be no question of their paramount value in 
indicating geographical and climatal con- 
ditions.” 
In 1882, Ward laid down in a definite 
and authoritative manner, the principles of 
geological correlation by means of fossil 
plants. He clearly showed that the old 
idea of contemporaneous deposits with 
identical fossils, as originally stated with so 
much prominence by Schimper and others, 
is entirely erroneous, and that it is relative 
contemporaneity or correspondence of suc- 
cession which must be considered, an idea 
which the late Sir William Dawson often 
laid great stress upon in the course of his 
discussions with the writer. In order to 
give proper expression to the idea of corre- 
spondence of succession, Ward has proposed 
and for several years has employed the ap- 
propriate term ‘ homotaxis.’ He lays down 
the general principles that 
