1913] COOPER—ISLE ROYALE 211 
place until light is admitted to the forest floor by the destruction 
of some of the present generation. 
The characteristic bog forest shrubs are the alders. Alnus 
incana is found principally near the bogward edge, while Alnus 
crispa, belonging rather to the climax forest, inhabits the landward 
portions. 
In the lower vegetation mosses are most prominent both in 
quantity and variety; 22 species were taken from a single area of 
bog forest. Sphagnum spp. (relicts of the open bog stage), Cal- 
liergon Schreberi (Willd.) Grout, and Hylocomium proliferum (L.) 
Lindb. make up the bulk of the moss carpet. Sharing the forest 
floor with these is Carex trisperma Dewey which, accompanied by 
C. leptalea Wahlenb. and C. tenella Schkuhr, forms dense green 
mats of considerable size. In some places Lycopodium annotinum 
L. covers the ground, and in others there is a rank growth of 
Equisetum sylvaticum L. As minor features there are certain herbs 
that particularly characterize the bog forest. The most numerous 
are Habenaria obtusata (Pursh) Richards, Listera cordata (L.) R. Br., 
Smilacina trifolia (L.) Desf., Phegopteris Dryopteris (L.) Fée, 
Mitella nuda L., Coptis trifolia (L.) Salisb., Viola incognita Brainerd, 
Petasites palmatus (Ait.) Gray. 
The outstanding feature in the later part of the bog succession 
is the telescoping of stages. The sphagnum-shrub stage (when 
present) is hardly well established before the bog trees enter, and 
immediately following them or often actually with them come the 
climax trees. The reason for the early establishment of the latter 
is found in the likeness between the bog soils and those of the 
forested uplands. Those of the uplands are nearly as peaty in 
texture and properties as are those of the bogs. The causes of the 
peatiness of the upland soils trace back to other factors: low 
evaporation rate due to low temperatures; poor drainage because 
of solid rock substratum; and probable paucity of certain types of 
bacterial and fungal life. It follows, the two soils being much 
alike, that whatever trees can grow upon one may exist also upon 
the other. 
5. Two types of bogs 
One of the numerous questions that could not be settled with 
entire satisfaction related to two fairly distinct types of bogs 
