156 TREE ANCESTORS 



Our southern hackberry, CeUis mississippiensis, which is the 

 only other familiar form here in America, is a somewhat smaller 

 tree, rarely over 75 feet in height, with a short trunk 2 or 3 feet 

 in diameter, spreading branches and a broad graceful head. Its 

 leaves usually have entire instead of toothed margins, and the 

 fruit stones are pitted instead of smooth as in the other form. The 

 southern hackberry ranges from southern Virginia to southern 

 Illinois and Missouri, and southward to Florida and Texas. 



The hackberry line is not certainly known earher than Eocene 

 times. It has been recorded from the Upper Cretaceous of Europe, 

 but the leaves so named belong in all probability to the unfamiliar 

 and unrelated genus Zizyphus. Two forms of hackberry are 

 recorded from the early Eocene of Wyoming, and there was a late 

 Eocene species in Georgia. None are known from as eaply a horizon 

 as this in Europe, showing how imperfectly its geological history 

 is known. The Oligocene had furnished three forms in France 

 and Italy and one represented by fruits in the western United 

 States. The Miocene record is more full, and comprises traces 

 of 9 different species widely scattered in central and southern 

 Europe, and present at that time in both Colorado and Wyoming. 



There were 4 Pliocene hackberries in Europe and Asia, but none 

 have as yet been discovered in the limited Pliocene plant beds of 

 North America. The Pliocene hackberry of France and Germany 

 appears to have been directly ancestral to an existing species found 

 from the Caucasus to Upper India, and a similar close affinity is 

 shown to this same form by the Pliocene hackberry found fossil 

 in Japan. Pliocene species are also known from Slavonia and 

 Indo-China. 



The rigors of Pleistocene times apparently killed off the hack- 

 berries in all except the extreme southeastern part of Europe, 

 although a fossil species of that age has been recorded from Hun- 

 gary. A doubtfully extinct species has been described from the 

 Pleistocene of Maryland, The common hackberry has been found 

 fossil in Virginia, and beautifully preserved and characteristic 

 stones of our southern hackberry have been found in the wind 

 blown Pleistocene deposits known as loess in Mississippi. 



