HOLLICK: BOTANICAL PROBLEMS AND PALEOBOTANY 189 
the science of ecology, and especially in connection with the problems 
of phytogeography, that the work of paleobotanists has been of un- 
expected value, in furnishing explanations of many puzzling facts of 
modern plant distribution. In this connection we may hark back to 
certain of the genera already discussed taxonomically and consider 
them in relation to their present geographic distribution. 
The genus Liriodendron is represented by one species in eastern 
and middle North America and one in eastern Asia. The two species 
of Sassafras have the same distribution. Of the two species of 
Nelumbo one has a range in America extending from New Jersey to 
Colombia and the other is Asiatic. What is the meaning of the 
occurrence of only two species representing each genus and each of 
the species in such widely separated regions? We can not imagine 
that a genus could originate two specific types independently, each one 
in a different part of the world, even in a single fortuitous instance; 
and it is almost as difficult to believe that a genus could originate in 
Asia and develop a single species which somehow subsequently mi- 
grated to America and there evolved into a different species, or vice 
versa. Discussions of the possibilities of evolution, mutation, and 
migration afforded theoretical but unsatisfactory explanations. The 
discoveries of paleobotany, however, supplied actual facts, and these 
showed that in all such instances the genera were formerly world-wide 
in their distribution as well as prolific in species. A single example in 
this connection is sufficient. Fossil remains of some twenty-five 
species of Nelumbo have been brought to light, from the United 
States, British America, Greenland, England, Holland, Germany, 
Hungary, France, Portugal, Egypt and Japan. The problem of the 
modern distribution of any such genus in two widely separated parts 
of the world, therefore, has nothing to do with any phenomena of 
evolution, or mutation, or migration in modern times. It is merely 
a matter of elimination of species in past times, throughout the inter- 
mediate regions where they formerly flourished. On the same basis 
may also be explained the geographic isolation of Sequoia with its two 
living species confined to a narrow belt on the western slope of the 
Sierras in California, and Taxodium with its three living species con- 
fined to the coast region of the eastern and southern United States and 
the northern part of Mexico. The discoveries of paleobotany have 
demonstrated that in past ages both of these genera included many 
species and that they were widely distributed. They flourished not 
only in similar latitudes to those in which they now occur, but also 
northward beyond the Arctic circle as far as exploration has been 
carried. The climatic conditions of the Ice Age exterminated them 
everywhere in the North. The mountain systems of the Eurasian 
