108 C. O. ROSENDAHL AND F. K. BUTTERS 



of glacial moraines — in the richest soils often mixed with decidu- 

 ous trees. The Norway pine (P. resinosa Ait.) occupied the in- 

 termediate types of soils and mingled more or less freely with 

 both the other species. 



Of the three species of pine in Minnesota, P. Strobus L. is the 

 one most capable of maintaining itself outside the evergreen 

 forest area and of forming isolated outposts. Numerous such 

 patches occur down the valleys of the St. Croix and Mississippi 

 Rivers as far south as middle Iowa and westward on many of 

 the tributaries of the Mississippi, 30, 40, and in a few cases even 

 50 miles back from the main valley. 



For the most part these outposts consist of a few trees, usu- 

 ally perched on rocky ledges toward the top of the river bluffs, 

 but now and then they form almost pure groves an acre or more 

 in extent. Occasionally single isolated trees occur in the dense, 

 deciduous forest of the north-sloping hills, but in general there is 

 no such general and intimate admixture of white pine and de- 

 ciduous trees as is common in parts of Wisconsin and Michigan 

 and in southern New England. So far as the authors have been 

 able to ascertain there are about thirty of these isolated patches 

 of white pine in southeastern Minnesota today. (See map.) In 

 a few of these only old trees have been observed, but in most of 

 them a few younger trees and seedlings occur, so that left to 

 themselves, they would in all probability maintain themselves 

 indefinitely. 



The other two species behave quite dilTerently from the white 

 pine in their distribution. Pinus resinosa Ait. stays well within 

 the general pine area except in the valley of the St. Croix River 

 in the vicinity of Taylor's Falls, where, with the other two species, 

 it forms an outpost a few miles beyond the general border of the 

 evergreen forest, growing on the exposed pre-cambrian diabase in 

 the river valley. The white and Jack pines, therefore, form the 

 skirmish line along practically the whole boundary of the pine 

 area, but it is very seldom that outposts of the latter appear be- 

 yond the general area. In fact, up till the summer of 1915 

 only three such stations were known, all of them less than 15 

 miles from the main pine line. (See map.) 



