MacMillan : shores at lake of the woods. 993 



The influence of vegetation in fixing the sand and gradually 

 building up the dune need not receive particular treatment 

 here. It is well known that by the establishment of a few 

 grasses or Artemisias at some spot a hill may be gradually 

 formed around them, their roots uniting the particles of sand 

 and eventually binding the whole mass together in a mound. 

 Over this the grasses continue to grow, the mound growing 

 with them. When large dunes are formed every thing may be 

 upon a large scale. For example, in the well known region 

 about Lake Michigan, in northern Indiana, more extensive 

 slopes, summits and pools are formed and here an entirely differ- 

 ent series of problems in ecologic distribution must be consid- 

 ered in so far as the sand encroaches upon areas previously 

 covered with vegetation of another physiognomic group. The 

 types of the large dune pools of Indiana with their character- 

 istic limnetic zones of Solidago were not observed at Lake of the 

 Woods. Such zones depend upon a greater general moisture 

 less exposure to the wind, owing to surrounding trees of pre- 

 dunal development, and a general higher temperature. Solidago 

 juncea found sparingly on the Isle aux Sables seemed rather a 

 plant of the summits than of the pool borders. At Lake of the 

 Woods there is no evidence that the Isle aux Sables is tenanted 

 by both dunal and pre dunal types of plants. On the contra^ 

 the shoreward side of the dunes seems rather to have become 

 modified from its original type, permitting at present strand 

 formations to develop. A very clear, sharp delimitation of 

 back strand and mid- strand may be seen in a view of this shore- 

 ward aspect of the Isle aux Sables in Plate LXXII. The mid- 

 strand is of a mixed Salix and Cornns variety and the back 

 strand is of the shrubby Populus type. 



MORASSES. 



This form of shore vegetation has been classified as attached 

 and detached, but really some of the apparently fixed morass 

 should be placed in the second group rather than in the first. 

 This is true of what is here termed anchored bog. For in this 

 formation a juxtaposition of plants may arise quite the reverse 

 of that in the ordinary attached morass. Such is the case 

 when a bog floating from one shore to another becomes at- 

 tached to the bottom with its originally lakeward aspect now 

 turned shoreward. Since the peculiarity of plant distribution 

 in such cases is conditioned upon the formation having moved 



