446 George E. Nichols, 



pennsylvanicum, and the predominance among the vascular plants 

 of ericaceous shrubs. The bake apple (Rubus CJiamaemorus) 

 is one of the most characteristic plants of dry bogs. The sur- 

 face of such a bog is hummocky, and except in wet weather 

 the springy substratum underfoot is quite dry. The hummocks 

 vary from one to several feet in diameter and from a few inches 

 to more than a foot in height.^® The depth of peat ranges up 

 to more than six feet over a fiat rock floor, while over depres- 

 sions it may be considerably greater. Pools of the sort charac- 

 teristic of wet bogs are found here also, but much less 

 abundantly. Except for these and scattered wet depressions, 

 whose vegetation and ecological relations are quite distinct from 

 those of the enveloping area of dry bog (see later), the surface 

 almost everywhere is overgrown by the xerophytic cushion- 

 forming sphagnums, associated with which, and locally pre- 

 dominant, are certain other mosses (such as Dicranum Bergeri, 

 Racomiirium lanuginostim, and Polytrichum juniperinum) and 

 fruticose lichens (notably Cladonia alpestris, C. sylvatica, and 

 Cetraria islandica). The moist hollows between the hummocks 

 are commonly colonized very largely by liverworts, such species 

 as Ptilidium ciliare, Cephalozia media, Lepidosia setacea, and 

 Mylia anomala, which constitute more or less definite societies. 

 The characteristic vascular plants of the dry bog association- 

 type are the following: 

 Picea mariana Cornns canadensis 



Larix laricina Andromeda glaucophylla 



Eriophorum callitrix Chamaedaphne calyculata 



Scirpus caespitosus Gaultheria procumbens 



Carex pauciflora Gayliissacia dumosa 



Myrica Gale Kalmia angustifolia 



Sarracenia purpurea Kalmia polifolia 



Drosera rotundifolia Ledum groenlandicum 



Pyrus arbtiiifoUa airopiirpnrca Rhododendron canadense 

 Rubus Chamaemorus Vaccinium Oxycoccus 



Empetrum nigrum Vaccinium pennsylvanicum 



Nemopanthus mucronata Solidago uliginosa 



" Ganong remarks ('98, pp. 138, 139), that these sphagnum hummocks 

 grow "in such rounded, radiating masses that it reminds one of the 

 Raoulia or 'Vegetable Sheep,' and the resemblance is yet closer when, 

 by drying, it assumes a grayish color." 



