25 (j prof. w. a. herds! an on the abundance 



Some Algje. 



On rocky or ston}' shores the most consjiicnous organisms after the 

 barnacles are the large brown sea-weeds — the various species of Fucks and 

 its allies in the littoral zone and those of Laminaria at and below low-water 

 mark. At Port Erin and Port St. Mary we have made many counts *, and 

 some weighings, of the plants of Fucks and of Laminaria cut off from 

 sample square feet in different regions, and also of the epifauna associated 

 with the Algse. Fucks is most variable, ranging from 2 to 352 stalks to the 



• 



ft • 



• 



Fig. 8. — Diagram showing distribution of Laminaria stalks in one square foot. The black 

 square in centre shows the area they would occupy if placed together. 



square foot. Laminaria is more constant ; our counts range from 6 to 36 ; 

 but in a typical area of Laminaria-coveved rock, such as on the lower 

 limestone reefs at Port St. Mary, the latter figure or anything about 30 

 stalks to the square foot is usual. As the stalks are on the average half an 

 inch in diameter, this distribution means that they are scattered from 1 to 2 

 inches apart over the square foot (fig. 8). 



The fronds of the Laminaria springing from the one stalk may be wide- 

 spreading, and anything from 3 to 6 feet in height. Moreover, they may 

 support an epifauna and epiflora of many molluscs, worms, polyzoa, 

 hydroids, and smaller Alga?. We have made a number of measurements 



t I am indebted to one of my students at Port Erin, Miss Catherine Mayne, B.Sc;, 

 for much help with these counts and for a series of diagrams like figure 8 illustrating 

 the density of distribution. 



