408 Proceedings Portland Society Natural History 



presence of numerous depressions (Figure 37) which are 

 filled with aquatic sphagnums. The vigorous growth of 

 these has prevented the encroachment of less hydrophytic 

 species and the consequent building up of the mat to the 

 general level. These depressions are very wet and mucky 

 and in addition to the mosses usually contain a few very 

 characteristic forms, of which Lycopodium inundatum, 

 Xyris earoliniana, Drosera longifolia and Utricularia cor- 

 nuta may be cited as examples. Bordering on this more or 

 less open portion of the bog is a zone in which larger shrubs, 

 such as Viburnum, Ledum, Xemopanthus and the red maple 

 occur and this is followed by a narrow fringe of black 

 spruces and larches adjoining the upland (Figure 38). 



In the other type of bog the mat has completely filled the 

 depression and usually becomes grounded. In these mature 

 bogs it is no longer possible to make out any zonation to 

 the vegetation, the sedges, shrubs, and trees growing inter- 

 mingled (Figure 39). The bog forest, consisting chiefly 

 of black spruce, larch and red maple, covers large portions 

 of such bogs and ordinarily represents a physiographic cli- 

 max, since the substratum is too wet for other woodland 

 types to come in. Where there are somewhat better condi- 

 tions of drainage a coniferous forest of red spruce and fir 

 may succeed and in such cases it is possible to observe bog 

 and upland species growing side by side. 



The marginal ditches, so common a feature of bogs else- 

 where, are comparatively rare in the Penobscot Bay region. 

 Where they do occur their vegetation resembles that of a 

 well-drained swamp in which such shrubs, as Ilex verticillata, 

 Rosa Virginia na, Rosa nitida, Spiraea latifolia and Rhodo- 

 dendron cana dense predominate, while the most frequently 

 occurring herbaceous forms are Osmunda cinnamomea and 

 Calla palustris. 



Association-types of raised bogs 

 The bogs discussed in the preceding paragraphs all be- 



