140 Pub. Puget Sound Biol. Sta. Vol. 2, No. 43 



of all these regions are of solid rock with occasional stretches of gravel 

 or boulders. The average vertical width of shore occupied by the Fucus 

 zone on east slopes was over 1.5 meters. This average includes the coves, 

 and the shores covered by wharves and by the Station laboratory, all of 

 which showed little or no Fucus. The average vertical width of shore 

 occupied by the Fucus zone on the south was over 2 meters, and on the 

 north less than % meter. The higher the shore on the north, northwest 

 and northeast exposures, the narrower was the Fucus zone. 



The following are some of the more pertinent facts observed in a 

 general study of various kinds of shores : 



1. Shores under overhanging trees have little or no Fucus. 



2. Average north shores have a very narrow Fucus zone. 



3. North exposures with a high shore-line have no Fucus zone. 



4. Exposures abounding in Fucus have none under wharves. Station 

 Laboratory, etc. 



5. The darker a cove the less Fucus on its shores. 



The graphs drawn from the measurements of the Fucus zone on both 

 sides of the Station and about Point Caution are shown in chart 1. It will 

 be noticed (chart 1) that the Fucus zone practically disappears under 

 the wharf and that there is practically none under the laboratory. Ob- 

 serve how narrow the zone is on north slopes. From this it appears that 

 light is a factor. 



Experiments were then set up with a view to determining the effect 

 of different light intensities on Fucus, and if possible to find how much 

 light was necessary for its growth. 



In order that the plants might be grown under different light in- 

 tensities four lath shade-crates were constructed. These were l^ "^- deep 

 and 1 m. square. Both top and sides were made of laths. The fraction 

 of the total area which was left as space between the laths was the frac- 

 tion of total daylight which could enter. The plants were left in their na- 

 tural habitat in all cases, and the crates set over them. With mature 

 plants the following series was arranged : 



1. Plants in total daylight, by leaving them wholly uncovered. 



2. Plants covered with a lath shade-crate, thru which only half the 

 light could enter. 



3. Plants covered with a lath shade-crate thru which only a fourth 

 the light could enter. 



4. Plants covered so that only an eighth the light could enter. 



5. Plants under inverted tubs, and thus in total darkness. 

 Heavy cords were tied to each upper corner of the shade-crates, and 



to each of these a heavy rock was tied. The rock rested on the shore. 

 This was security against the action of the tides. The tubs were held 



