MacMillan : shores at lake of the woods. 1019 



crevice plants, while between the crevices the rock is bare or 

 maintains at best a few lichens and mosses. Upon high wind- 

 swept rock shores at Lake of the "Woods an occasional odd eco- 

 logic adaptation of the white pine is to be observed. Instead 

 of growing in the ordinary way the plants lie flat like a Juni- 

 per and cover sometimes circles thirty yards in circumference 

 with a dense low network of prostrate branches. One would 

 scarcely recognize the plant as being Pinns strobus at all, ex- 

 cept upon close investigation. 



The crevice- tree formations are shown prettily in Plate 

 LXXVIIT in the background, on the left, where a steep smooth 

 rock shore bears a vigorous crevice flora of Pinus strobus of the 

 ordinary form and Pinus divaricata. Among the innumerable 

 islands of the lower lake this type of shore is exceedingly 

 common. It is well developed also in Shoal lake and in White- 

 fish bay. Of the shores of the upper lake fewer are of this 

 type, but some of the Northwest Angle inlet and Moose bay 

 shores are perfect examples. 



When a crevice-tree formation arises in a crevice running 

 parallel with the shore-line the drainage often brings about 

 the building of a concentric soil ridge, the trees serving as 

 barriers to the general downward drainage from the back 

 country, and thus a considerable zonal distribution may come 

 into existence. When, however, the crevices run perpendicu- 

 lar to the shore-line such a condition does not arise. This 

 origin of forest zones by drainage on dome-shaped islands, I 

 have considered fully elsewhere 10 . 



Perpendicular rock shores. The distribution of plants upon 

 precipitous cliffs such as those of Crow Rock island is not 

 necessarily azonal. It has already been shown how an Endo- 

 carpon lichen zone may originate within the space of wave 

 activity while above, other lichens, Biaioras and Cladonias, may 

 become established. Yet upon the bold smooth face of a cliff 

 for the greater portion of its surface only azonal or biologically 

 zonal distribution of lichens, mosses, ferns and small crevice 

 plants is ordinarily to be observed. In some cases large crev- 

 ice-trees may es-tablish themselves upon these precipitous 

 faces. The most abundant plants, however, upon the precipi- 

 tous cliffs, in all this region, are lichens of the .genus Thelo- 

 schistes. One may with propriety consider this as a typical 

 formation. 



10 MacMillan : Distribution of plants, etc. I.e. 



