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 



