5 68 
Sinnott and Bailey . — The Origin and 
separated regions as the Antarctic continent, England, India, and North 
America have so very many plants in common that the essential uniformity 
of the vegetation all over the earth at that period is generally admitted by 
geologists. The succeeding flora of the Cretaceous displays almost as great 
a uniformity in its composition. Not only were these floras homogeneous, 
but they appear to have flourished under much more equable conditions 
than those now prevailing over most of the earth. The occurrence far north 
of the Equator of so many warmth-loving plants such as Cycads, Ferns, and 
Palms, which are not adapted to resist cold, and their association in such 
regions with other species now characteristic of the temperate zones, indicates 
that low temperatures were unknown and that the climate was probably 
devoid of any wide extremes of heat or cold. Very few regions of the earth 
in modern times, save perhaps certain oceanic islands, exhibit climatic con- 
ditions resembling those of the Mesozoic ; but the absence of extreme cold, 
which seems above all else to characterize these ancient climates, is to-day 
found only within the tropics. If such conditions at present favour the 
development of woody rather than herbaceous Angiosperms (as our tables 
have shown), it seems to be a reasonable conclusion that in ancient times 
as well they would have tended to produce a predominance of ligneous 
plants, and that the Angiosperms at their inception were in consequence 
mainly or entirely woody. 
If we assume, then, that woody plants were originally the dominant 
type of dicotyledonous vegetation throughout the world, the question arises 
as to where herbaceous forms were first developed and what were the causes 
for their origin. The present distribution of herbs throughout the various 
regions of the world provides important evidence for the solution of these 
problems. 
2. Development of Herbaceous Forms in the North Temperate Zone. 
Since herbaceous plants attain their highest predominance to-day in 
the great land -mass of the north temperate zone, this region must have seen 
a more profound change in the growth-habit of its vegetation than any 
other, if our theory is correct. We should expect, therefore, to find some 
evidence that in past times woody plants constituted a more important 
feature of the flora of this region than they do at present, and such evidence 
is, in fact, forthcoming. 
In the first place, it has been shown that during Cretaceous and 
Tertiary times very many genera and even families of trees flourished in 
the north temperate zone which are either absent or rare in this area at 
present, but of which many still occur in warmer regions. The presence of 
Ficus, Eucalyptus, Diospyros , Cinnamomum, Aralia, and various Proteaceous 
genera as fossils in Northern Europe or America may be cited as an 
example. 
