■V. THE VERTICAL DISTRIBUTION OF THE SPECIES. 



If we walk along the beach at low-tide we see a belt laid bare, 

 the breadth of which varies according to the degrees of declivity 

 of the coast and according to the tides — that is according to 

 whether it is spring-tide or neap-tide. At spring-tide the belt is 

 broad and at neap-tide narrow. The low-water mark of neap-tide 

 divides the belt laid bare into two parts, an upper part which is 

 laid bare during every low-tide and a lower part which is laid bare 

 only at and about spring-tide. The upper part, between the upper 

 limit of growth of the algal vegetation and the low-water mark of 

 neap-tide, which almost coincides with the lower edge of the Fucacece- 

 belt, I call the Upper Littoral Zone. The lower part, from the 

 lower edge of the Fucacece-beli to the usual 1 low- water mark of 

 spring-tide, I call the Lower Littoral Zone. Below low-water mark 

 of spring-tide begins the vegetation which is constantly submerged. 

 That the vegetation of the lower littoral zone is closely connected 

 with that in the upper part of the constantly-submerged zone is 

 natural and will be discussed subsequently. 



In the following table a dash ( — ) denotes a habitat (depth) in 

 which the species has been found many times, and a dot (•) one 

 in which it has been found either once or comparatively rarely. 



Table 7. The Vertical Distribution of the Species. 



Litto 

 ral 



Depth (metre) 



Rhodophyceae. 



1 Bangia fuscopurpurea 



si Porphj'ra mlniata 



1 No notice is taken of the extraordinarily low ebb-tides which occasionally 

 occur and by which large Laminarice are often exposed. 



