i6o 
G. R. WI ELAND 
Keuper) age. But in the original list there are four species of Thinnfeldia, 
which are probably ginkgoid, and if so considered would reduce the Filicales 
to a more normal proportion. Further tabulations of Mesozoic plants 
may be found in Volume 2 of my "American Fossil Cycads." 
As in the case of the Dinosaurs, the cycadeoids after they reach relatively 
high specialization, move rapidly toward extinction during the phase of 
continental development which begins with the great epeiric seas of the 
upper Cretaceous submergence and ends in the full continental areas of the 
glacial stages and later or present arid climates. This is the period, not of 
angiosperm origins, but of angiosperm dispersal and specific modification 
with disappearance also of the early or transition angiosperms. 
One other observation, and the subject of distribution may be left aside, 
it hardly being practicable to go into moot questions of generic distribution 
for the moment. In almost all instances the doubtful border of cycadeoid 
foliage ends in a tree forest of seed ferns, Cordaites, pines, Araucarias, and 
Ginkgos, but never in recognizable scrub. With the legitimate inferences 
from stem structure, and the characters of Wielandiella, and especially of 
Williamsoniella in mind, a much greater Mesozoic forest comes into view. 
Nothing in paleobotany appears more probable now than that amongst the 
cycadeoids will be found the lost forests and the greatest forest makers of 
the Mesozoic. 
II. Relationships 
If the systematist can recognize a degree of relationship or similarity 
between the monocot arums and screw pines, and the Ranalean dicots, 
why is not oblique or inequal convergence the more difficult explanation? 
Those resemblances must have been still greater in the Jurassic forest. 
But even then these several lines must have been distinct. Nothing has 
so limited progress in phylogeny as the potting of " paleontologic trees." 
If more attention were given to the elementary facts of the record as found, 
progress in its interpretation would be surer. For whether, in that lofty 
mood, variation is held to be epigenetic, or orthogenetic, or whether it be 
held that there is less of continuity and that the main course of biologic 
change goes on in select lines and types with much outright extinction, 
both the object and the method of phylogenetic study remains the same. 
The primal object is to determine the order in which structures and organs 
appear, and thus to find how the groups of animals and plants are related 
in time. From any more philosophic viewpoint classifications are only 
made to serve this purpose, and thus afford a sound basis for the more ulti- 
mate study of variation. And therefore, while classification is at every 
stage in the development of plant study a serious task, classifications them- 
selves should be viewed as wholly impermanent. As a definition of classi- 
fication, then, may be given, simply, present views of relationship. 
In attempting to elucidate some of the principles which must influence 
