780 The American Naturalist. [September, 
woody trunks and branches,—and in Conifer in the evergreen 
foliage,—ready to burst forth with the first coming of warmth. 
Diclinism is most frequent in the spring months,—where this 
occurs in the lower groups of plants the case is covered by the 
general principle; but when diclinism obtains in highly 
specialized forms, as a result of retrogressive evolution, the 
problem becomes difficult,—the interesting question suggests 
itself: Does reversion in structure here revert the flowering 
period to an earlier season? As a case in point, recall the 
genus Carex. Again, there is a determining function in the 
character of the flower's habitat :—The spring flowers seek 
largely the protection of the woodlands; marsh-plants reach 
perfection mainly in latest spring and shrough the summer, 
though some, like Caltha, are early; the aquatics of ponds and 
river glory in the summer sun; and the flowers of meadow 
and prairie and thicket-margin luxuriate from mid-summer to 
the end of autumn. This last recalls the recent observations 
of Conway McMillan on “ tension-line flora," and we note with 
interest that the highly organized tension-line flora gives us 
our later blossoms to a large extent. Further, every practical 
botanist knows that the herbaceous flora of summer, as a whole, 
shows a great advance in vegetative luxuriance over the corre- 
sponding flora of spring. But it does not follow that that of 
fall in turn advances, for vegetative luxuriance means 
primarily—heat. Yet the truth remains that this is not the 
fundamental criterion of plant aristocracy,—in the giant cal- 
amite of geologic ages flowed humbler blood than flows to-day 
in the dandelion of our backyard grass-plots. So each new 
factor that arises, far from weakening, but adds significance to 
the fundamental principle. 
Here the question rises: Why should there be a correspond- 
ence between the course of the flower seasons and the system 
of floral evolution? Solve this, and the “ philosophy of flower 
seasons" is an open riddle. But for the present it is only 
possible to indicate the direction in which the answer prob- 
ably lies: The most simple and generalized forms, coming 
first in the course of floral evolution, have had the longest time 
in which to adapt themselves to existent climatie conditions; 
