986 MINNESOTA BOTANICAL STUDIES. 



is shown (Plate LXX), where the back country is shrub and 

 meadow. In such Salix back strand S. nigra is a conspicuous 

 species together with S. amygdaloides, but the former is more 

 abundant. 



XI. Quercas arboreal back strand. The prevalence of small 

 trees of Quercus macrocarpa is sometimes so considerable upon 

 certain shores that one is justified in discussing the group as 

 a distinct back strand formation. I find it at Lake of the 

 Woods characteristic of rather low, rounded and fertile shores. 

 Wind exposure if not too great seems not an unfavorable con- 

 dition. Sometimes an irregular contour of the shore may be 

 maintained without prejudice to the Quercus formation, but in 

 such cases the mixed arboreal type is more likely to be de- 

 veloped. 



XII. Mixed arboreal back strand. When the surface con- 

 tour is irregular, the soil fairly fertile, the shore not too low, 

 and the wind activity not too pronounced a mixed forest may 

 develop. In all such cases it is difficult to delimit the back 

 strand from the general back country vegetation and such 

 mixed arboreal back strand indicates slight topographic 

 specialization of the back strand ridge. Upon low shores, 

 sterile shores, regular shores, inundated shores, shores ex- 

 posed to occasional surf and spray, this type to of formation 

 seems not to develop readily. 



This brief discussion of the different back strand formations 

 which are on the whole most easily distinguished as such, for 

 purposes of description, at Lake of the Woods, may be ter- 

 minated at this point with a recapitulation of the conditions 

 under which development seems ordinarily to progress. 



1. Gramineous back strand: Slopes, low elevation, rounded 

 contour, slight exposure to wind. 



2. Mixed herbaceous back strand: Soil with power of re- 

 taining moisture near the surface. Considerable humus-con- 

 tent. 



3. Coniferous shrubby back strand: Absence of inunda- 

 tions, shelter from winds, sterile soil and coniferous back 

 country neighboring formations. 



4. Populus shrubby back strand: Low sterile soils, strong 

 wind currents; spray, infrequent inundations. 



5. Salix shrubby back strand: Low, inundated, nitrogen- 

 ous soil, slight wind currents. 



6. Rosaceous shrubby back strand: Higher shores, stronger 

 winds, absence of inundations, fairly high humus- content of 

 the soil. 



