CHAPTER XIV 



The Elm, Planer and Hackberry 



The elm family is known scientifically as the Ulmaceae, the name 

 being derived from the Latin Ulmus, which was the classical name 

 of the European elm, said to have been derived from the Celtic 

 elm. Like so many other tree famihes the elm family offers much 

 of interest to students of geographical distribution and its bearing 

 upon geological history. Strange as it may seem to those who know 

 only our familiar elms of the shaded malls and streets of our New 

 England towns, the elm family is a largely tropical group, although 

 the elms themselves are inhabitants of the Temperate Zone except 

 for their occurrence in the mountains of tropical Asia. 



The family contains about 15 genera and considerably over 150 

 species, of which less than one half belong to the elms and hack- 

 berries, which, with the single unique planer tree of our southeast- 

 em States, are the only members of the family native in the United 

 States. To the botanist the problem of the absence of elms and 

 hackberries and the presence of 3 other genera in Africa is 

 difficult to explain, as is the absence of elms and true hackberries 

 in South America where there are four other genera of the family 

 represented. A similar unsolved problem is the range of the genus 

 Solenostigma from the Mascarene Islands to Polynesia and its 

 absence in Africa, or the presence of Zelkova in Asia Minor and 

 the Caucasus and its reappearance in northeastern China and 

 Japan ; or why the hackberries range from the Atlantic to the Pacific 

 in the United States when the equally ancient elms are not found 

 in our west. Many facts pointing toward the solution of these 

 problems have been derived from the study of fossil plants, but 

 unfortunately no traces of many of the genera of the elm family 

 have as yet been found in the rocks. For example a genus like 

 Trema found at the present time in Africa, Asia, Austraha and 

 South America e\ddently had a long geological history since it 



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