3 College of Forestry 
Plant Life of the Tertiary Periods. The Age of Elabora- 
tion or Differentiation of Modern Elements and Aspects 
of Vegetation in Response to Differentiating Environ- 
ment. 
It was, as others have stated, indeed a revolutionary change 
which, in the early Cretaceous period saw the dawn of the 
present in plant life when angiosperms appeared, and a fore- 
cast of wonderful possibilities of development when these 
became so dominantly established in the later Cretaceous. 
These possibilities seem to have been realized in great full- 
ness during those periods of the Cenozoic era, known, at least 
to botanists, as the Tertiary. 
It is always a thrilling experience to watch the bursting 
forth of plant life in the spring when vegetation is expressing 
itself in varied aspects of vital activity and in myriads of 
forms as it takes up its yearly active relation to the manifold 
aspects of its environment. There are two sides to this great 
process of unfolding and adjustment. On the one side, the 
surging energy of life in its rebound after dormancy, applied 
through the individuality which distinguishes every plant 
species and indeed every single plant. On the other side the 
environment, involving all the aspects of climate, of soil, of 
different forms of animal hfe impinging on plant life at 
every point and of the many sided relation of plants to each 
other. 
Now this sort of thing is what I have in mind when I ask 
you to imagine the differentiation of plant life and of its 
environment as it seems to have taken place most notably 
during the Tertiary periods. As to the plant life, you get a 
partial measure of what came about when you consider (1) 
The apparently innumerable species of dicotyledonous and of 
monocotyledonous plants representing hundreds of genera 
and scores of families whose finer distinguishing characters 
are based largely aS the apparently bewildering diversity 
of flower structures. (2) What seems an equally bewildering 
diversity of growth forms already referred to on page 24. 
(3) The segregation of plant life into wide floral provinces 
from tropical to arctic divisions, and of vegetation into di- 
