CHAPTER XVII 



The Sweet or Red Gum and Witch Hazel 



The sweet gum belongs to a family, often called the witch hazel 

 family (Hamamelidaceae), whose present geographical distribution 

 is of remarkable interest. The family comprises 19 genera in all 

 and about 50 living species, and no less than 9 of these genera are 

 monotypic, that is to say, they are each represented by but a 

 single existing species. 



Monotypic genera are either geologically old or else very modern, 

 that is, their single species may have been recently evolved or it 

 may represent the last remaining descendant of a long and now 

 extinct hne, and it is usually possible to get some idea as to which 

 of these categories we are dealing with by a consideration of the 

 present geographical distribution of the different members of a 

 plant family. In the case of this family 12 of the 19 genera are 

 confined to Asia, 1 is prevailingly Australian, 3 are African and 3 

 are confined to Asia and southeastern North America. 



Both the sweet gum and the witch hazel belong to this last 

 category, their present range being shown approximately on the 

 accompanying sketch map (fig. 39). It is obvious that a distri- 

 bution such as this indicates that the family to which they belong 

 had an extended geological history and that the particular genera 

 once flourished in regions that connect the present discontinuous 

 occurrences. The only alternative is to suppose that the present 

 disconnected areas of distribution represent special creations — which 

 is absurd, or to suppose that the same genus originated independ- 

 ently on different continents, which is almost equally absurd. The 

 details of the geological history of the witch hazel family are for 

 the most part unloiown because of the imperfection of the geological 

 record. 



THE S\^^EET OR RED GUM 



No part of the Temperate Zone can compare with southeastern 

 North America in the brilliancy of autumnal fohar display and a 



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