998 MINNESOTA BOTANICAL STUDIES. 



shore area. Very beautiful exhibits of zonal distribution are 

 often afforded upon shelving shores provided with morassic 

 formations. Ten or twelve distinct zones of plants will be de- 

 veloped as the moisture content of the soil diminishes from the 

 edge of the water, inland. Plate LXXVI shows four of these 

 zones; a Scirpus zone nearest the water edge, a Salix zone 

 farther inland, a Betula zone behind this and finally aLarix zone 

 backed by trees of Pinus strobus, the latter not belonging, how- 

 ever, in this case, to the true shore group. 



Floating bog. Coming next to the consideration of detached 

 morass it should be observed that such does not develop under 

 quite the same conditions as does the permanently attached 

 morass. The following are favorable conditions for the forma- 

 tion of detached morass. 



1. A smooth surfaced bottom without the numerous crevices 

 or irregularities that would assist roots to hold fast and thus 

 keep the morass in place. 



2. More exposed situations, at the heads of broad or ex- 

 tended bays, where higher winds can arise and hence more surf 

 energy would be developed, tending to separate the morass 

 from the shore behind. 



3. A higher percentage of floating plants in the original 

 morassic composition, as for example, Particular ias, Utricularias, 

 Potamogefons, Lemnas and others in which a considerable por- 

 tion of the plant body, if not the whole, is natant. 



4. More precipitous shores where the detachment is shar- 

 per and easier than if the bottom shelves gradually. 



5. Weak places in the morassic texture where, owing to 

 some zone of detachable plants, the whole lakeward mass can 

 be removed from the shoreward portion. Such a line may be 

 be called the scission line of the formation. 



Under a variety of conditions, especially when they co-oper- 

 ate, morassic areas may be detached and carried into deeper 

 waters. In some of the lakes of Minnesota these floating bogs 

 are very prominent features and constitute the so-called "float- 

 ing islands." At Lake of the Woods they do not seem to be 

 abundant. The best specimens observed are in Northwest 

 Angle bay, Moose bay and Four Mile bay behind Oak point. 

 As developed, the floating bog comes to have some characters 

 peculiarly its own, due to the moving about in the water and 

 the removal from the particular point of attachment. The 

 peculiarities of the floating bog are these: 



