MacMillan : shores at lake of the woods. 973 



ture of the mid -strand will have fallen several degrees below 

 that of the back strand, as observations made in 1894 very 

 clearly indicated. The occasional inundations, surf, winds 

 and spray all combine both directly and indirectly to lower 

 the temperature of the mid-strand substratum so that plants 

 requiring a somewhat higher root temperature like Polygona- 

 him, Viola, Anemone, Vagnera, do not in this region venture 

 down upon the light cold sands, but remain where intermixture 

 of humus, shelter from winds and evaporation, and darker 

 color of the soil, all cooperate in preserving more nearly an 

 optimum temperature. 



In general the mid- strand area studied at different points on 

 Lake of the Woods appears to afford an excellent example of 

 the sensitiveness of plant formations to varyiDg environmental 

 conditions. The character and aspect, the abundance or pau- 

 city of certain forms, the arrangement of the different forms 

 with reference to one another all seem definitely conditioned 

 upon the variations in exposure, slope, temperature, moisture, 

 wind-currents and surf-impact, or upon combinations or modi- 

 fications of these. So the constant variety of the beach as one 

 walks along it is connected with the multitude of variations in 

 the soil below, the air above and the water off shore.. The mid- 

 strand, too, is modified by the back strand which abuts upon it. 

 By the population of the back strand its own is changed, and 

 by the struggle that goes on in the back strand the mid-strand 

 may in time be affected, as when rows of trees grow to a great 

 height on the back strand thus shading a portion of the mid- 

 strand. And by the physical texture and contour of the back 

 strand, the mid-strand may be affected very sharply — as when 

 the rain is carried through gullies in the back strand down up, 

 on or across the area nearer the water's edge. Curious inter- 

 rupted patches of Carices and Epilob turns that occur in the mid- 

 strand are often to be referred to declivities or gullies of the 

 back strand, directing the moisture to some spots rather than 

 to others. Thus both the physical and biological conditions of 

 the zone farther inland affect the beach flora quite as dis- 

 tinctly as do the conditions shoreward. 



Back strand. — The back strand is commonly marked by a 

 considerable rise in elevation and must generally be regarded 

 as developed principally by the activity of the wind rather 

 than by the surf or ice. Such ridges behind the mid-strand are 

 usual, and in some cases no doubt are of more ancient develop- 



