Igo9] COULTER—EVOLUTION AMONG GYMNOSPERMS 83 
The Paleozoic groups Cycadofilicales' and Cordaitales represent 
the historical background of gymnosperms. They are of equal 
age, so far as the records are available, and are’so connected by inter- 
grading (or rather anastomosing) forms that their relationship seems 
evident. The Cycadofilicales are so fern-like in every feature except 
their seeds, that their derivation from some ancient fern stock 
(called provisionally Primofilices) is as certain as phylogenetic con- 
nections can be. The origin of the Cordaitales, therefore, presents 
two alternatives: either they arose independently from the same 
ancient fern stock, or they were differentiated from the Cycadofilicales 
very early. To choose between these alternatives is not very impor- 
tant, but the latter one seems to be the more reasonable, because the 
Cordaitales (as we know them) are much more removed from the 
ferns than are the Cycadofilicales. If this conclusion is accepted, it 
follows that gymnosperms began with Cycadofilicales more ancient 
than any yet known; that Cordaitales branched off from Cycado- 
filicales earlier than our present records; and that the two groups 
constituted the extensive gymnosperm flora of the Carboniferous. 
This Paleozoic display of gymnosperms was succeeded by a 
Mesozoic display, in which at least four groups are recognized. From 
the Cycadofilicales there arose the Mesozoic Bennettitales and the 
Cycadales; and from the Cordaitales the Mesozoic Ginkgoales and 
Coniferales were derived. The Bennettitales have been traced almost 
to the Paleozoic, and their structure, as well as the habit of some of 
the earlier forms, make their connection with the Cycadofilicales 
appear convincing. The relation of the Bennettitales to the Cyca- 
dales is not so clear; either the two groups were differentiated from 
# common stock that arose from the Cycadofilicales and continued 
Into the Mesozoic, or the Cycadales were differentiated early from the 
Bennettitales. The records show that the Cycadales are much younger 
