176 
Champlain period. The more difficult problem is the explanation of their 
persistence. 
A consideration of a few other species will serve to emphasize the 
point in mind. 
The Larch or Tamarack (Larix laricinad (DuRoi) Koch) is found in 
Porter, Marshall, Kosciusko, Noble, Steuben, DeKalb and Blackford. An 
examination of the older shore lines of Lake Michigan gives a sufficient 
explanation. Even the Blackford County citation, which seems well to the 
south, is made clear when the ancient bay of Lake Michigan extending 
southward through Allen County in the neighborhood of Fort Wayne is 
recalled. 
Thus also the eastern Peach-leaved Willow (Salix amygdaloides An- 
derson) found in Lake and Kosciusko finds ready interpretation, as does 
also the case of the Wild Red Cherry (Prunus Pennsylvanica Linnzeus fils) 
occurring in Lake, Porter and Kosciusko counties. 
Any one who maps some of the more widely ranging species of the 
State will be immediately impressed by the close relations existing be- 
tween the distribution of the species and the course of waterways. In 
some instances the distribution follows a single waterway, in others it 
seems to follow not merely the main stream but also all of the tributaries. 
Indeed, by far the most striking feature in the series of one hundred 
twenty-six maps is the definite way in which this relationship stands out. 
The most cursory inspection of the maps reveals it and serves to suggest at 
least a possible causal relation. 
In the opinion of the writer the occurrence of given species in widely 
separated localities without intervening stations will be found to be due to 
the existence at some time in the past of practically continuous waterways 
connecting these now separated localities. Further, that such connections, 
in so far as the region under consideration is concerned, are mainly to be 
found in the Champlain period, although perhaps in some cases this con- 
nection was furnished by the northward stretching arm of the Gulf of 
Mexico. If the shore lines of streams and lakes of the Champlain period 
could be drawn upon our present maps many of our problems in Phytogeog- 
raphy would solve themselves. In contirmation of this view is the dominat- 
ing influence of continuous waterways or of streams in the distribution of 
species clearly shown by any careful study of present range extensions. 
In the main, widely ranging species, at least among trees, do not have 
