Development and Distribution of Vegetation. 51 
species of these trees, Sequoia gigantica, the largest, and S. sempervirens, the 
most abundant, They occur nowhere else in the world, except as planted by 
man. They have no near relatives. There is no apparent reason in the pecu- 
liarities of the climate or soil to account for this extreme isolation; yet there 
must be sufficient reason for the fact. Curiously such relatives as they have 
are also peculiar in their distribution. One of them is the bald cypress of our 
Southern states ( Zaxodiwm distichum) occurring no where else, and the other 
is a Glyptostrobus, similar to the cypress, in China. Here are four trees con- 
stituting a tribe, two in California, one extending from Maryland to Mexico 
and the other in China. 
Before passing further in the account it may be well to note similar facts in 
regard to other trees. A tree belonging to the genus Torreya grows along the 
shores of a single river in Florida, another occurs in California; while finally 
another species is a native of Japan and the Himalayas. Furthermore, in 
each of these three regions a yew grows, and yew trees are not found elsewhere 
except in Europe. Surely there must be some good cause for this state of 
things. The comparison by no means ends here. The relationship of the 
floras of our Atlantic states and of eastern China and Japan is indeed closer 
than those of the eastern and western shores of the American continent. Now 
relationship means community of descent. There it no other meaning for it. 
Ordinarily when only a few species of a peculiar type exist, they are to be 
looked for in the same country; when it is not so we wonder why. 
Let us not now fall into the old error of imagining different ‘‘centres of 
creation” to explain facts of distribution. Who would think of the white 
inhabitants of Cape Colony as an original population deriving autonomously 
their English-like appearance, habits and industries? or who, finding a com- 
munity composed of Russian mennonites in Dakota would separate them in 
kindred from those of the Czar’s dominions? In such cases migrations are at 
once thought of as explanation. Why should we not think of this.in regard 
to plants? Appealing to fossils for help, the case of the California redwoods, 
with which we began, becomes clearer. It has already been remarked that in 
the rich Tertiary beds of Greenland remains of Sequoias have been found. 
This is also true of Spitzbergen, Iceland, the Mackenzie River country, of 
Alaska and of other Rocky Mountain regions. Fossils have also been ob- 
tained from various parts of Europe, even well southward. As identified there 
formerly were at least six species of Sequoia in the arctic zone, some of which 
spread over large areas in Europe and North America. Instead therefore of 
their present systematic and geographical isolation, their ancestors formed great 
portions of immense forests, covering wide areas of land. The glacial cold 
destroyed them or pushed them southward along territory adapted to their 
growth. In Europe and perhaps in Eastern America barriers cut off their 
retreat. The mountain chains of Southern Europe down whose slopes great 
glaciers pushed towards the plains, together with the Mediterranean sea effect- 
ually blocked the southward march, and annihilation was inevitable. Not so 
with the Rocky mountain system, which stretched to the southward and fur- 
nished, step by step, a highway of refuge. The Taxodiwm and Glyptostrobus 
pushed southward in the same way, survived in different localities, the one in 
America the other in Asia — though they formerly inhabited the same region 
at the north. It would be mere speculation to attempt to give in detail the 
reasons why Sequoia survived only in western, Zaxodiwm in eastern America, 
and Glyptostrobus in Asia; but their present isolation ceases to be mysterious 
after the explanation now given. That the explanation is not a mere accident 
of these species is abundantly shown by the study of other kinds. The cli- 
matal conditions of Europe is certainly as favorable for the numerous kinds 
of trees of varying hardiness as that of the Atlantic states of our Union; but 
the fact is that in our forests are found 66 genera and 155 species of trees, . 
