52 Development and Distribution of Vegetation. 
while Europe has only 38 genera and 85 species. Since the introductions by 
man, England alone has at least double the species that can survive in the 
Atlantic states. 
Why this relative poverty of the European forests? Abundant proof exists 
that it was not always so. The Tertiary fossils show that Europe did have 
most if not all our genera and at least as many species. Why they were lost 
has been sufficiently explained if the Sequoia history is true. The similarity 
of the oaks, the chestnuts, the maples, the lindens, etc., is also explained in 
the same manner, and no other adequate reasons have been produced. Not 
only forest trees, but the main elements of the floras of the extra tropical 
northern hemisphere have a similar romance in their pedigree. To-day 
climatal conditions dominate vegetation; but he who would seek to know- 
much of the present distributions of plants must acquaint himself with the 
vegetation of former epochs and eras of plant life on the Earth. 
By taking a wider survey of the vegetation of the Earth the fact becomes 
more positive and conspicuous that during the long ages of their existence 
plants have been distributed from one end to the “other of the globe. One 
hundred and fifteen European genera of flowering plants are found in New 
Zealand, excluding those introduced by, or through the agency of man. 
Among these fifty-eight species are identical. Not less surprising is the fact 
that one hundred and fifty species are common to Scandinavia and the Atlan- 
tic United States. Between sixty and seventy genera of northern plants are 
found in South America south of the lower portions of Chili; and about an 
equal number have representatives in South Africa. 
The causes that have produced this world-wide distribution have been great . 
cosmical fluctuations, involving enormous alternations of warm and cold cli- 
mates, with variations in the terrestrial currents of air and water sweeping 
over wide continents and through immense oceans. He who would understand 
all about the migrations of plants must rise to a knowledge of the history of 
the Earth during, at least, a score of millions of years. 
