94 The Irish Naturalist. February, 



most striking and delightful features of the vegetation of the 

 island. Certain tall herbaceous perennials are abundant in 

 the Bracken areas, more on account of the shelter from wind 

 which there obtains, than of the shade which the Bracken 

 gives — such are the Red Campion {Lychnis diurna), Agri- 

 monia odorafa, and Cow-Parsnip {Hcracleiim Sphondylhun).. 

 On the steep northern sea-slopes, as about Saltpan Bay, where 

 the sun but seldom strikes, the shade plants are reinforced by 

 large quantities of Male Fern {Laslrea E?7ix-mas), growing 

 luxuriantly quite open to the sky and sea, and mixed with 

 great L,ady Ferns {Athyrium Filix-fczmma). Many of the 

 procumbent root-stocks of the Male Fern are three feet in 

 length. 



The Heath Associatio?is. 



The highest parts of the island are generally occupied by 

 heath. The upward dying out of the Bracken is undoubtedly 

 often due to exposure, since along its junction with the 

 heather it is constantly seen filling the hollows, while Heather 

 crowns the surrounding knolls. But other influences are at 

 work, since, in some places (see map), the Heather descends 

 to the coast-line, breaking through the enclosing cordon of 

 Bracken. Probably these lowland patches of heath cover a 

 soil too shallow for the creeping rhizomes of Pteris. The 

 absence of deep soil would appear to be, as regards the change 

 from Bracken to Heath, a factor equally important with that 

 of exposure to wind. Only two Ericaceae occur on the island 

 — namely, the Purple Heather {Erica cincrea) and the lying 

 {Calluna vulgaris), and these two appear to be usually in direct 

 competition for mastery on the heath areas. Sometimes 

 Erica is absolutely dominant — this is usually on the steeper 

 and more rocky places. Elsewhere it is so much reduced in 

 quantity that an almost pure Callunetum results. Over much 

 of the area the two species are mixed in more or less equal 

 quantity. Calluna appears to stand exposure better than its 

 congener, and often forms ragged bushes rising from a closer 

 lower growth of E. cinerea. Hypmtm cuspidatum is the most 

 abundant moss of the heath area, and Cladonia rangiferina 

 the commonest lichen. These two are the only abundant 

 species which can be classed as dependent; but there is a 



