MacMillan : shores at lake of the woods. 1003 



a bed of humus soil or at least highly nitrogenous sand for most 

 favorable growth, Polygonum grows vigorously in crevices 

 and may be described indeed as a crevice-plant, rooting under 

 water. The stout stem, long pennant-like leaves, suggesting by 

 their position in time of wind the well known aspect of Phrag- 

 mites, and strong attachment to the bottom make this plant an 

 able cumaphyte although, it is true, it cannot structurally be 

 regarded as the equal of Scirpus lacustris. 



Barriers in light surf. Of these three types are repre- 

 sented at Lake of the Woods. 



I. Phragmites barrier. This, with Phragmiies phragmites 

 as the dominant plant, which is of cosmopolitan distribution in 

 regions of light surf, is well developed on the shoreward face 

 of Scirpus barriers, and very often exists without the Scirjius 

 fringe, in coves and protected bays. It cannot, however, 

 exist off a shore where the surf is heavy unless protected by a 

 Scirpus zone. The formation is well developed near the mouth 

 of Rainy river and in the Northwest Angle bays. 



II. Spiraea barrier. The plant is Spiraea salicifolia, a 

 species as noted above, with wide range of habitat, and 

 characteristic throughout the Lake of the Woods region as a 

 crevice plant on rocky shores. It commonly grows submerged 

 a few inches and occupies a zone inside of the Polygonum- zone, 

 thus bearing often the same relation to Polygonum that Phrag- 

 mites does to Scirpus. With its stiff stems, slender long leaves 

 and firm roots, it withstands a considerable washing of the 

 waves and seems to flourish well although submerged for a 

 considerable portion of the summer. In autumn or in mid- 

 summer the water falls below its spring level and the foothold 

 of the Spiraea becomes dry. The peculiarity of structure in 

 the plant which enables it to grow partly submerged or in dry 

 rock crevices fits it particularly for the extreme shores of rocky 

 islands, and here, as for example on the southern points of 

 Oak island it grows abundantly. 



III. Salix barriers. Like the Spiraea barrier this is connec - 

 ted with fluctuations in the lake level. The components are 

 members of the genus Salix, but one species in particular, Sa- 

 lix fljsViamis is most prevalent as a surf barrier. The habitat 

 chosenis off drift-shores, the plant seeming to prefer a region of 

 sand to one of rock- crevices or submerged humus. Consequently 

 since rocky islands with drift dropped upon one shore and not 

 upon the shore opposite are common in Lake of the Woods, it 

 often happens that a zone of Salix will be established at the 



