E. V. Wulff — viii — Historical Plant Geography 



of continental drift, Proc. Roy. Soc. Edinb. B, 6i, II (13),?. 149 et seq. 1 941), others take 

 violent exception to it (see Bailey Wans, On the Life History of Theory, Am. Scientist 

 30:290, 1942). 



From a purely botanical standpoint I compiled certain data from the published volumes 

 of the second edition of the Englee-Prantl "Natiirliche Pflanzenfamilien", in which all 

 the known genera, approximating 2811 in all the families of the Gymnospermae, 26 families 

 of the Monocotyledoneae, and 95 families of the Dicotyledoneae are considered. Only about 

 180 of these 2800 genera have species common to both hemispheres. This is a good 

 case of random sampling as the groups considered include many famiUes of plants that are 

 strictly tropical, and many such as the Pinaceae, Cupressaceae, Liliaceae, Saxifragaceae, 

 Rosaceae, Cruciferae, Caryophyllaceae, and others, that are very well developed in the tem- 

 perate zone with a fair number of representatives even in the far north. The genera that 

 are common to both hemispheres are but about 6.3 percent of the total. Were strictly 

 tropical groups considered, it would be much smaller. I merely cite these figures for what 

 they may be worth, but were the theory of drifting continents correct one would logically 

 expect to find a great number of genera common to the tropics of both hemispheres. 



The editors of Chronica Botanica are under obligations to Dr. 

 H. M. Raup, of the Arnold Arboretum, and to Dr. and Mrs. Stanley 

 A. Cain, of the University of Tennessee, for their assistance and advice 

 in preparing the present text for the press. 



The appearance of this volume at this time emphasizes the fact that 

 science is not limited by international boundaries and that the work of 

 one investigator prosecuted in one country under one regime, contrib- 

 utes materially to the advancement of knowledge in all countries. I 

 should like to quote a statement of Mr. Raymond Fosdick in a recent 

 report of the Rockefeller Foundation: "In the shadows that are deepen- 

 ing over Europe the lights of learning are fading one by one. The 

 conception of knowledge as an international responsibility has vanished. 

 The free flow of ideas across boundary lines between laboratories and 

 universities had dried up. Elsewhere the exigencies of war have erased 

 the opportunities for intellectual and cultural life as that term was 

 understood a few years ago." And yet, in spite of the war, and in 

 spite of the fact that the U. S. S. R. has suffered most grievously, it 

 has been possible to provide for the English translation of the present 

 volume in Russia, and its publication in the United States of America. 



The author. Dr. E. V. Wulff, was born in 1885. He received his 

 Ph.D. degree from the University of Vienna in 1910. He is well known 

 for his publications deahng with historical plant geography, on the 

 flora of Crimea, various phases of economic botany, and systematic 

 work on the Scrophulariaceae. He is Curator of the Herbarium, De- 

 partment of Geography of Cultivated Plants of the Institute of Plant 

 Industry of the U. S. S. R., Leningrad. 



Appended to this foreword is a statement prepared by Dr. Hugh 

 M. Raup of the Arnold Arboretum, in which various significant papers 

 are listed, supplementing the numerous references given by Dr. Wulff. 

 Most of these appeared in the interim between the publication and 

 revision of the original Russian edition and this EngHsh translation of 

 Wulff's work. 



Elmer D. Merrill 



Jamaica Plain, Mass., U. S. A. Adminislrator of Botanical Col- 



ChmSTMAS, 1942 lections, Harvard University, and 



Director of the Arnold Arboretum 



