36 College of Forestry 
The attempt will be made to show that diversity or variety 
in vegetation aspects reflects a like diversity of habitats. 
This idea seems to find pointed application in connection with 
the Tertiary elaboration of plant life now under considera- 
tion, for during that time and especially toward the close of 
the Tertiary, great changes took place in the surface of the 
land. “ On the whole” (quoting Chamberlin and Salisbury, 
IIT, 316) “ the close of the Pliocene must be looked upon as 
a time of great crustal movement, a critical period in the 
history of North America. New lands were made by emer- 
gence from the sea and old lands were deformed and made 
higher ; new mountains were made and old ones rejuvenated. 
Streams were turned from their courses in some places and 
nearly everywhere started on careers of increased activity.” 
These changes would be assumed to play a significant role 
at a time when plant life had come into the peculiarly plastic 
and responsive stage represented by the oncoming wave of 
angiosperms. 
Angiosperms and the Significance of Flower Structures. 
The terms “ seed,” “ angiosperm” and “ flower ”’ are asso- 
ciated with revolutionary changes in the program of plant 
life so that, while we may not go into technical details which 
would suffice to distinguish, fundamentally, nonseed-bearing 
from seed-bearing plants and so on, it must be said that the 
“drift” or, biologically stated, the course of evolution was 
toward more certain and effective production of vigorous 
progeny by plants. With the coming of seed plants, a 
strategic point had been gained in that the origin and develop- 
ment of a new individual and in considerable measure, its 
opportunities for becoming separately established, came 
to be under the care and nurture of the mother 
plant. Nor was embryo production any longer lm- 
ited to certain special conditions where sperms could 
reach the ege only through the agency of water, as for 
example in ferns, but a new process, pollination, could be 
effected through the air and at any height above water level. 
