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lands frequently inundated during the year, or in low moist localities. We 

 find that the larger part of them, in their mass distribution follow the 

 swamps of the Atlantic or Gulf coast, or of both. It is very evident also 

 that the extension of range northward must have occurred when similar 

 physical conditions existed ; that is, either at the time the Gulf of Mexico 

 stretched an arm far into the north, or if a later date is preferred in the 

 time of the flooded rivers and lakes of the Champlain period. Occasional 

 means of transportation may serve to explain occasional cases, but where 

 species become component parts of a forest in a region apparently remote 

 from their mass distribution a different explanation must be sought. 



Six species, so far as the records go, are confined to Lake, Porter and 

 Laporte counties or to some one of them. In this region, also, extremely 

 skillful and persistent work has been done by Rev. E. J. Hill, a fact which 

 should be taken into account. The species peculiar to this region are the 

 following : 



Pinus Banksiana Lambert. 



Thuya occidentaJis Linnaeus. 



Betula populifolia Marshall. 



Betula papyrifera Marshall. 



Alrms ineana (Linnaeus) Muenchhausen. 



Geltis pumila (Muhlenberg) Pursh. 



The Jack or Scrub Pine [Pinus Banksiana Lambert! occurs in Lake 

 and Porter counties, where it is fairly common on the sand dunes border- 

 ing Lake Michigan. The general range of this species is decidedly north- 

 ern, the Indiana stations representing in all probability its extreme south- 

 ern limit. In our area it is an undersized, rather shrubby form, maintain- 

 ing itself with difficulty. The continuity of waterways is the evident 

 explanation of the occurrence of this species in the Indiana tree flora. 



The Arbor- Vitae or White Cedar (Thuya occidentalis Linnaeus) appar- 

 ently occurs native only iu Lake County. This characteristic species of 

 northern swamp regions is found only in cold swamps of our area. There 

 seems no good reason why it should not be found in similar situations in 

 other counties bordering Lake Michigan. The form has been so extensively 

 planted for windbreaks and for ornament that many incorrect citations are 

 on record. Its presence as a member of our flora is evidently referrable to 

 continuous waterways furnished by the Great Lakes. 



The Gray or White Birch (Betula populifolia Marshall) is found in 



