.'3.'36 Proceedings Portland Society Natural History 



these may be mentioned Danthonia compressa, Lechea inter- 

 media, Pyrus melanocarpa, Potentilla trident at a, Solidago 

 bicolor, S. nemoralis and the mosses, Polytrichum commune 

 and P. juniperimim. In addition to these species, which are 

 almost universally present, other forms may locally be 

 prominent. One tract of granite has a crevice vegetation 

 composed entirely of Juncus Greenei and Polytrichum (Fig- 

 ure 4). On an exposed serpentine hill on Little Deer Isle, 

 the crevice plants are chiefly ferns, such as Asplenium 

 TricJw manes and Woodsia ilvensis. 



Heath-mat association-type 



As the lichen mat, above referred to, develops it becomes 

 more and more difficult to distinguish the crevice plants, for 

 many of the species are now able to find a foothold in the 

 larger amount of soil afforded by the mat and they rapidly 

 spread over the surface. The lichens are still a prominent 

 feature (Figure 5), but they are soon dominated by the 

 higher plants, particularly the heaths and the resulting as- 

 sociation is known as the heath-mat. J uniperus communis 

 var. depressa is often conspicuous at this stage (Figure 6), 

 while other characteristic species present on the mat in- 

 clude : 



Herbaceous Plants 

 Pteridium aquilinum Lechea intermedia 



Selaginella rupestris Aralia hispida 



Deschampsia flexuosa Cornus canadensis 



Arenaria groenlandica Lysimachia quadrifolia 



Potentilla tridentata Prenanthes trifoliata 



Shrubby Plants 

 Pyrus melanocarpa Vaccinium pennsylvanicum 



Rhododendron canadense Vaccinium Vitis Idaea 

 Kalmia angustifolia var. minus 



Arctostaphylos Uva-ursi Viburnum cassinoides 

 Gaylussacia baccata 



