962 MINNESOTA BOTANICAL STUDIES. 



the earth, no longer seems a matter of chance but rather the 

 definite result of definite, although endlessly complicated 

 causes. 



Advantages offered by a fresh-water archipelago in the 

 study of ecologic distribution. — It has long impressed the 

 "writer that a lake with numerous islands offered one of the best 

 fields for research in ecologic distribution and with this belief 

 in mind, Lake of the Woods was selected as a peculiarly excel- 

 lent body of water for study. The advantages are many. 

 Portions of land of convenient size for careful and exhaustive 

 examination are, in such an archipelago, isolated one from 

 another by areas of water. Lake of the Woods offers a wide 

 variety of shore-lines varying from the mud-flats of the mouth 

 of Rainy river and Muskeg bay to the sand-dunes of the Isle 

 aux Sables, the extended beaches of Oak point and the North- 

 west Angle, the drift mantled shores of Garden island, the 

 rounded rocks and talus heaps of the smaller American islands 

 and the cliffs and crags of the Crow rock and Shoal lake 

 islands. Almost every kind of shore-line from floating bog to 

 precipice may be observed, and, from the exceptional shape of 

 the lake, exposures to narrow, secluded channels, through 

 which the frail canoe of the Indian or the voyageur creeps with 

 difficulty, may be considered at one point, while at another one 

 may stand before a roaring surf without even a distant haze of 

 land visible at the horizon's edge. But for the monotony of 

 its silicious soils such a lake with its thousands of islands, its 

 cliffs and morasses its winding bays and its Grand Traverse 

 would be an ideal spot for the solution of most of the intimate 

 problems of ecologic distribution. 



DERIVATION OF THE PLANT POPULATION. 



General considerations. — It may be laid down as a law of 

 plant distribution that the hinds of plants in a region depend 

 upon general causes originating at a distance and of long dura- 

 tion, while the position, number and strength of plants depend 

 upon local causes of shorter duration. Thus the presence of 

 the white pine, P. sfrobus, in the Lake of the Woods region 

 rather than P. taecla of more southern and eastern range results 

 from a long evolutional history, to comprehend which thor- 

 oughly would require an extended survey of vegetation condi- 

 tions both of to day and of the past, over a great portion of the 

 continent of North America. But the position of plants of P. 



