MARINE ALGAL VEGETATION 



97 



low-water mark of neap-tide, and is exposed during each low- 

 tide; the upper littoral zone is, then, the littoral zone proper, 

 which doubtless corresponds exactly with Kolderup Rosenvinge's 

 limitation of the littoral zone in Greenland, but not entirely with 

 Borgesen's limitation of the littoral zone in the Faeroes, as some 

 of the Faeroese littoral associations seem to belong to the next belt. 



The semi-littoral zone extends from about the low-water 

 mark of neap-tide to a depth of about 10 metres, and thus extends 

 over the lower littoral zone, and even lower than that. In reality 

 this zone comprises the lower littoral zone including stragglers below 

 the low-water mark of spring-tide to a depth of 10 metres. That 

 part of the zone lying in the lower littoral zone is laid bare at and 

 about spring-tide, but is submerged at neap-tide. 



The sublittoral zone extends from the low-water mark of spring- 

 tide to the absolute depth-limit. 



There seems to me to be no reason for calling any part of the 

 Benthos elittoral. Even if the 40-metre contour is a lower limit of 

 growth in the case of several species, and is, approximately, the 

 lower boundary of the La/nz'naWa-community, yet the upper bound- 

 ary of the red-algae communities which extend further downwards 

 than 40 metres lies much higher, and the 40-metre contour thus 

 cuts straight through natural communities. It cannot, therefore, be 

 considered the principal boundary as regards the whole of the 

 constantly-submerged vegetation. Stromfelt (I.e.) is of the opinion 

 that, possibly, elittoral vegetation does not exist on the coasts of 

 Iceland. According to Kjellman the elittoral vegetation is extremely 

 poor in species, and probably has a limited distribution everywhere 

 in the northern seas. From what -has been said above respecting 

 the 40-metre line, and from a comparison with Greenland (Rosen- 

 vinge, 63) and the Faeroes (Borgesen, 11 and 12), it is obvious 

 that a division of the constantly-submerged vegetation at this depth- 

 line is not quite natural in the northern seas. It is more correct, 

 therefore, to do as Rosenvinge and Borgesen do, and to class 

 the vegetation as sublittoral down to the absolute depth-limit. 



In the following I do not employ the term "region," which is 

 now generally used to describe somewhat limited subdivisions of 



The Botany of Iceland. I. 7 



