MacMillan: SHORES AT LAKE OF THE WOODS. 967 



affinities of the Lake of the Woods population are rather with 

 the general group of plants distributed throughout the Red 

 river valley and in southern Minnesota than with the series 

 lying in the same latitude but to the eastward of the Rainy 

 lake region. Bailey's list of plants collected on Hunter's 

 island is especially instructive in this comparison. In this 

 list of 80 species such varieties as Carex lenticular is, Aster 

 macrophyllus, Spiranthes gracilis, Ahuis viridis, Oeum nivale, 

 Habenaria orbiculata, Alnus incana, Gaultheria procumbens, 

 Myrica gale, Corylus rostrata, Anaphalis margaritacea, Thuya 

 occidentalis and others serve to indicate the strong northern 

 character of the plant population of this district. And upon 

 the shores of Lake Superior where such genera as Pinguicula, 

 Bibes, Drosera, Diervilla, Antennaria and Pyrola are strongly 

 developed in number cf individuals a quite different cast is 

 given to the general flora. This is to be explained without 

 doubt as in part a result, as has been indicated above, of the 

 recession of the waters of the glacial lake Agassiz from south 

 to north, thus opening up the ancient bed to infiltration of 

 southern forms. Thus there may be observed the very inter- 

 esting occurrence of Celtis occidentalis for example on the 

 dunes at Lake of the Woods where it grows in company with 

 Sorbus sambucifolia and Juniperus sabina. Similarly inter- 

 esting is the appearance of Ambrosia psilostachya as a dwarfed 

 but characteristic denizen of talus and boulder drift shores on 

 Big island point, and the abundance of southern species of 

 Sagittaria in strand pools, surrounded by I?*is, Polygonatum 

 and Allionia. 



DESCRIPTION OP PLANT FORMATIONS. 



Classification of formations. — In entering upon a discussion 

 of the variety of formations that may be observed upon shore 

 areas at Lake of the Woods, I shall make use of the division 

 proposed in a recent paper upon the distribution of tamarack 

 and spruce in bogs 7 . Formations may be broadly grouped as 

 Zonal, where the topographic feature presents a well-marked 

 radial symmetry, and Azonal. where the topographic fea- 

 ture presents no well-marked radial symmetry. A further 



7. Macll Ulan. On the formation of circular muskeg in tamarack swamps. Bull 

 Torr. Bot. Club. £3: 500. PI. 279-281. 1806. 



