972 



thus one maj' find, for example, a very moist crevice side by side 

 with one that is quite dry. 



3° Destruction of the roots and olher injuries will frequently 

 result from the steepness of the cHlTs, and altogether the habitat 

 may be far from being a stable one. 



4*^ In consequence of the steepness of the chfts, cHmatic factors 

 may have a very marked influence — wind, Hght, lieat and expo- 

 sure generally, also intense cold with absence of snow. 



5^ ClitY vegetation is protected from the grazing and trampling 

 of animals by its inaccessibility, but on the other hånd it is de- 

 prived of any manuring which might result (this of course does 

 not apply to the vegetation of sea-fowl cliffs, referred to later). 



l'hese and other factors tend naturally to the evolution of cer- 

 tain features distinctive of the chomophytes. The more noteworthy 

 among these are, that the roots as a rule strike deep and are very 

 vigorous, that the majority of the piants are spot-bound, while 

 many are succulent, also that the individuals are often tall and 

 remarkably vigorous in growth. On the other hånd the external 

 conditions present such wide variations, that it is not possible to 

 regard the chomophytes as a single natural unit in the same sense 

 as moor-plants, heath-plants, etc. 



The faet that the amount of water varies exceedingly in the 

 cliff vegetation must be specially emphasised; this before all others 

 is the factor which has the greatest influence, and is the first and 

 most imporlant condition in differentiating between plant-associations 

 with the same geographical and topographical position. It would 

 therefore be most natural to base the grouping of the different 

 forms of cliff vegetation on the water-content of the substratum, 

 and thus follow the method employed for the other associations. 

 It must be granted, however, that this is a method fuU of difficul- 

 ties in the case of the cliffs, since the amount of water varies so 

 much from place to place. The difficully in preparing a salisfactory 

 survey of a landscape so rugged as the Færoes, where the forma- 

 tions displace one another with bewildering frequency, becomes a 

 still greater difficulty as regards the cliff vegetation, which may be 

 compared to a variegated mosaic set in a homogenous matrix, the 

 solid rock. 



Some divisions can, however, be recognised, and these lie rcady 

 to hånd in certain descriptive names already in common use amongst 

 the inhabitants. These designations generally have reference to 



