594 A. HESSELBO 



Jnncus and Carex tiifts, and this formation must most neaiiy be 

 termed a Iransitional form l)et\veen moss-healh and meadow-land. 

 On the whole, Rhacomitrium canescens thrives hest in Iceland on 

 somewhat damp ground, under quile similar conditions as Aula- 

 comniiim tiirgidiim. 



The Mixed M o s s- h e a t li {Hylocominm - Rhacomitrium heath) 

 occurs especially on slightly inclined gravelly flåts, under similar 

 conditions as the healher moor, and is, as a rule, a pioneer for 

 the lalter. It may, however, also develop into a grass or heri) 

 slope, where the ground is wetter. The chief species of this moss 

 carpet are Rhacomitrium canescens, R. hypnoides and species of 

 Hylocomium, but as a rule many other species are found intermixed 

 with these. 



In a moss-heath near Modruvellir (Esja), on a slightly inclined 

 gravelly flat, at an altitude of about 100 metres, the chief species 

 of the Bryophyte carpet were Hylocomium proliferum, Rhacomitrium 

 hypnoides, R. canescens and Hypnum uijcinatuni; more scantily oc- 

 curred: Hylocomium loreum, H. squarrosum, Cliuiacium dendroides, 

 Antitrichia curtipendula , Brachythecium albicaus, Polytrichum alpi- 

 nnm, P. urnigerum, Timmia austriaca, Pohlia cruda, Ditrichum flexi- 

 canle, Bartramia ilyphylla, Dislichium montainim, Ptilidium ciliare, 

 Frullania Tamarisci, Lophozia lycopodioides, L. quinquedentata and 

 L. quadriloba. Scatlercd in the Bryophyte carpet grew a few flowcr- 

 ing piants such as Anthoxanthun^ and Galium verum, and this 

 moss-heath will undoubtedly develop into grassland. 



On a flat inlerspersed with stones at an altitude of about 

 400 melres the Bryophyte carpet was composed of Rhacomitrium 

 hypnoides abundanlly mixed with R. canescens, Hylocomium parie- 

 tinum, Hypnum uncinatum and Dicranum Starckei. As an inter- 

 mixture in the Bryophyte carpet occurred: Timmia austriaca, Pohlia 

 con^mutata, Dislichium montanum, Lophozia quinquedentata, L. qua- 

 driloba, L. alpestris, Plagiochila asplenioides , Blepharostoma tricho- 

 phyllum, Anthelia Juralzkana, Alicnlaria scalaris, Cephalozia pleni- 

 ceps and C. bicuspidata. Flowering piants were almost entirely 

 absent. 



On prominent kiiolls of earth occurring on heathland and 

 grassland, on dry ledges and slopes, a ver}^ peculiar Bryphyte 

 covering is often found: low, very compact cushions of /.)//:»/i{/sc»;/7? 

 sessile in connection with several livervvorls, esi)ecially Gymnomi- 

 trium concinuatum, are found covering the soil with a very dcnse 



