rinee 



A - Coralline 



B- Sub-littoral fringe 1 Cowes 



C - Mid-littoral fringe | Bay 



D- Supra-littoral fringej 



E - Hatfield's beach 



F - Mudstone 



G - Mid-littoral 



H- Supra-littoral fringe^ 



► Kawau 



Limits of standard 

 error of estimate 



0-100 0-200 0-300 0-400 0-500 



Outside diameter of bladder (inches) 



„ . , Thickness 



Thickness TOO 



100 



B 



4 Hrs. 



1-5 2-0 2-5 SxSea 

 — * Increasing Cone 



Fig. 209 A, Rate of water loss per hour in Hormosira. (After 

 Bergquist.) B, decrease in diameter of cell walls when placed in sea 

 water of increasing concentration. C, decrease in diameter of cell 

 walls under normal conditions of exposure. An = Ascophyllum 

 nodosum^ Ff = Fucus spiralis var. platy carpus, ¥s=Fucus serratus, 

 Fv = F. vesiculosus. (After Zanefeld.) 



These cell walls decrease in thickness when subjected to desic- 

 cating conditions, and the higher a fucoid is growing on the shore 

 the more the cell walls ultimately shrink on drying; so it must be 

 assumed that a large part of the water lost is contained in the cell 

 walls (Fig. 209B5 c). Those species which lose water most slowly 

 will also reabsorb it most slowly and, as a result, the growth rate of 

 the highest species will therefore tend to be the slowest. It would 

 appear that a major factor controUing zonation, so far as these 

 fucoids are concerned, is the biochemical nature and properties of 

 the cell wall, although it is also possible that these features have 



389 



