DISTRIBUTION AND RELATIONSHIPS OF THE CYCADEOIDS 1 57 
As a rule, more is known of the vertical range or persistence in geologic time 
than can possibly be learned of the lateral range for a given period. And in 
nearly all fossils the probable period of extinction is more determinable than 
the first appearance. This follows for several citable reasons, and especially 
in the case of plants. Nearly everything, moreover, depends on the habitus 
of the plant, and upon where it grew. Generally the three thousand species 
of coal plants appear cosmopolitan because in the Carboniferous certain 
coastal plains were peculiarly favorable places for conservation, and now the 
economic value of coal so abundantly laid down leads to vast excavation 
over hundreds of square miles of the rocky strata, and through thousands 
of feet in thickness. How different is the case where some Permian, 
Rhaetic, or mid-Triassic horizon is studied. The excavation for material, 
then depends on the enthusiasm of about a dozen men, taking the world 
over. This explains almost in a word why the record in the Carboniferous 
seems extensive, and in later periods much scantier. 
It has long been held that cycads or Cycadophytes, as now more broadly 
named, dominated the Jurassic especially. But probably botanists, who 
have outnumbered paleobotanists a hundred to one, have generally been 
taken aback on noting that the score or more of well-marked post-Carbon- 
iferous floras seldom include more than loo species in all. And on compar- 
ing, for instance, the Liassic of Scandinavia, England, India, and Mexico, 
it is even more disquieting to find that the species look stereotyped, as if 
they belonged to a few nearly related groups and gave but a vague picture 
of contemporaneous vegetation. But here the graver difficulties end. Ex- 
cept in the case of the Mesozoic gymnosperm stems, vast in quantity, of 
rare beauty of conservation, and urgently demanding study, the paleo- 
botanist quite invariably deals with larger features. Just as the microscope 
reveals histologic detail, so separation in time magnifies structural and other 
changes to the point of visibility. 
Thus far there appears to be no great fallacy in taking the cycadeoids 
from a generalized point of view and by percentages observing their ratio 
of abundance to the other forms of the successive horizons. This is in 
effect a rough consensus of plant life taken from age to age. The results 
are of course open to different interpretations, and it is most difficult to 
draw lines between all of the greater groups. In going back there is a 
gradual mergence of Coniferophyte, Cycadophyte, and Ginkgophyte foliage 
toward the seed-bearing quasi-ferns, at once indeterminate and startling to 
observe. Then very far toward the early Paleozoic there seems to be some 
kind of contact between the early seed ferns, and the older Lepidophyte 
types also leading toward the primitive gymnosperms. As to whether, 
well down in the Devonian, some of the Lepidophytes of the Pseudobornia 
alliance were in near contact with Archeopteris, and like the later seed ferns 
also led into the primitive Coniferophytes, is the real sphinx riddle of 
paleobotany — far more so than the origin of the angiosperms. It looks 
