90 BOTANICAL GAZETTE. [ April, 
a range extending north and east of our state, and that those 
south and southeast are found mostly on mountains, proves that 
the temperature of the arctic regions, where our flora originated, 
was some cooler during the cretaceous period than that of In- 
diana at present. As the same laws which now produce the warm 
equatorial current from the southwest prevailed during the ter- 
tiary period, no doubt the same difference in temperature between 
the eastern and western coasts of America existed then and ex- 
tended much farther inland, owing to the absence of such high 
mountain ranges to break the force of the warm current. Dur- 
ing the Champlain epoch, therefore, when these plants were seek- 
ing to escape the heat, they moved in an easterly as well as north- 
erly direction. 
It will be noticed that a much larger proportion of those 
plants belonging to the south southwest and southeast is limited 
by Indiana than of those from the north. This is caused by the 
natural barrier to northern progress presented by the Great 
Lakes and also by the fact that any plants remaining in or reach- 
ing the Mississippi valley will be very liable to be borne south 
by its river currents, so that a plant which is most abundant in 
the north may be found scattered along the banks of the Missis- 
sippi as far south as climate will permit its growth. 
The Polypetale, Gamopetale and Monocotyledons have near 
the same proportions in thedifferent directions and about that given 
i table for all; while the Apetale, of which there are only 
one hundred and thirteen in Indiana, have 32% of their number 
southeast and the next largest number east—which in the table 
means along the eastern coast, but not so far north as Canada or 
south as Florida. 
Among the Polypetale the Leguminose have the largest num- 
ber in the southeast and next along the eastern coast from Canada 
to Florida, while the Rosaceze are most abundant north and along 
the eastern coast respectively. 
* Composite among Gamopetale have the largest number 
southeast, while those along the eastern coast are about as numer- 
ous. 
Among Monocotyledons, however, the Cyperacee and the 
Graminex especially have a very large proportion common to all 
North America, or at least to the United States and far north 
into British America. Perhaps the mode of growth and repro- 
duction of these families will partially account for their wide dis- 
tribution. 
