Hill: Penobscot Vegetation 359 



reach well toward the high tide limit. On the rock surface 

 where the seaweeds are absent several lichens may occur, 

 notably Verrucaria mucosa, growing where it is submerged 

 at every tide ; and at a little higher level Verrucaria maura. 

 Occupying the area beyond the reach of the ordinary 

 tides, but swept by spray during storms is another zone, the 

 supralittoral. The lower portion of this is practically de- 

 void of vegetation, but the upper portion is occupied by 

 lichens, chiefly Caloplaca elegans, Caloplaca murorum, 

 Caloplaca baumgartneri, and Xanthoria parietiria. In 

 the crevices of this area herbaceous plants first make their 

 appearance. Characteristic forms include: 



Hordeum jnbatum Ligusticum scothicum 



Carex hormathodes Coelopleurum actaeifolium 



Iris setosa var. canadensis Plant ago decipiens 

 Sagina procumbens Solid ago sempervirens 



Sedum rosea m Senecio sylvaticus 



At the summit of the bluffs there is often developed a mat 

 of prostrate or low shrubs, chief among which are the trail- 

 ing juniper (Juniper us horizontalis ), common on bare 

 rocks, and the crowberry (Empetrum nigrum), where there 

 is a peaty turf. This latter plant may form large mats 

 which extend out from the edge of the turf and hang down 

 over the face of the cliffs. Other conspicuous species oc- 

 curring on the crests are the poison ivy (Rhus Toxicoden- 

 dron), bayberry (Myrica carolinensis), bearberry (Arcto- 

 stapliylos Uva-ursi), mountain cranberry (Vaccinium Vitis- 

 Idaea var. minus), and Juniperus communis var. depressa. 

 Between these shrubs grasses are common, chiefly Festuca 

 rubra, Danthonia compressa, Deschampsia flexuosa and 

 Trisetum spicatum var. molle, the latter two often growing 

 in the Empetrum mat. Various halophytic seed plants, 

 more common on beaches, may also be present, both on the 

 crests of the bluffs and in crevices on the face. This area 

 of prostrate shrubs does not always occur for its presence 

 and extent is determined by the degree with which trees have 



