Skinner: TIDE POOL VEGETATION OF PORT RENFREW. 155 



II. In general the higher the elevation of the pool and the 

 less exposed to wave action, the fewer the species found, though 

 the number of individuals may be abundant. 



III. The more gradual the slope and the rougher and more 

 irregular the sides, the more abundant the plant life. A per- 

 pendicular or receding wall is unfavorable for the location of 

 plants. 



IV. The presence of pebbles and loose rocks on the bottom 

 of a pool prevent the distribution of plants over the bottom or 

 far down the sides of the pool. 



V. Pools which are subject to a strong vortex action are more 

 or less completely circular in outline. 



Where the waves enter quite uniformly from the same direc- 

 tion the pool is usually elongated in the direction of movement 

 of the wave. 



The work on tide pools, as outlined above, must be considered 

 in no sense complete. Several conditions which have an influ- 

 ence on tide pool vegetation have received no consideration in 

 this article. The effect of temperature ; the effect of illumina- 

 tion ; the condition of the water in regard to its salinity ; the rate 

 of repopulation of a pool from which all plant life has been re- 

 moved and a comparison of the tide pools of the different rock 

 formations occurring at Port Renfrew readily suggest condi- 

 tions, the investigation of which should prove both interesting 

 and profitable. 



