LUTHER BURBANK 
of the north pole. During the so-called Mesozoic 
age, the conditions of the northern hemisphere 
were those that would nowadays be described as 
tropical or sub-tropical. There were palms grow- 
ing in Europe, and such species as the sequoia, 
the plane trees, maples, and magnolias grew even 
at a relatively late period as far north as the 
seventieth degree of latitude. Remains of conifers 
have been found within nine degrees of the pole 
itself; remains of palms in Alaska coal measures, 
and of the sassafras along the western coast. 
At this early period the flora of the entire 
northern hemisphere was, as regards its trees, 
essentially comparable to the existing flora of 
America to-day. 
There were oaks and beeches scarcely dis- 
tinguishable from existing species. 
There were birches and planes and willows 
closely related to the living species known as Salix 
cambida. 
There were laurels not unlike their modern 
representatives, the sassafras and cinnamon tree, 
and myrtles and ivies that are represented by 
existing. descendants of allied forms. 
And there were magnolias and tulip trees of 
which the existing tulip tree of the United States 
is an obviously direct and not very greatly modi- 
fied descendant. 
[182] 
