vf 
for the study of shallow rock pools. The far-reaching 
effects of varying proportions of exposure and sub- 
mergence are revealed by a careful study of the pool 
flora and of the inter-pool vegetation of this area. 
The area may conveniently be divided into four zones, 
as follows :— 
ZONE I. Exposed 5% to 25% of the tidal period. 
ZONE 2. Exposed 25% to 50% of the tidal period. 
ZONE 3. Exposed 50% to 75% of the tidal period. 
ZONE 4. Exposed 75% to 95% to the tidal period. 
Increasing length of the period of submergence shews 
_ corresponding rise in frequency of occurrence for individuals 
of a species, and a marked increase in the number of 
Species present. 
The commonest species obtainable are :— 
ZONE I (Plate II). 
Enteromorpha intestinalis 
Prasiola stipitata 
Uvospora isogona 
Ralfsia verrucosa 
Scytosiphon lomentarius 
Corallina officinalis 
Lithothamnion Lenormandi 
ZONE 2 (Plate VI). 
Lithothamnion Lenormandi and Corallina officinalis (co-dominant) 
Ulva latissima 
Cladophora spp. 
Codium mucronatum 
Ceramium rubrum (epiphytic on Corallina) 
Caliithamnion arbuscula (epiphytic on Corallina) 
Plumaria elegans (epiphytic on Corallina) 
Rhodymenia palmata (occasional) 
In Zones I and 2 there is no inter-pool vegetation. 
ZONE 3 (Plate III). 
From the beginning of Zone 3 downwards towards the 
sea the inter-pool vegetation becomes increasingly 
evident. The commonest plants in this area are :— 
