1918 Gail; on Fucus 149 



contained diatoms also. Diatoms maj^ be harmful but they are not a de- 

 termining factor. 



SUMMARY 



1. Mature Fucus plants are more resistant to lower light intensities 

 than are sporelings. 



2. Desiccation of young plants is believed to prevent the growth of 

 Fucus on gravel. 



3. Reduced light intensities cause the death of well-grown Fucus 

 plants 1 m. below the surface of the water. 



4. Well-grown Fucus plants receiving less than 1/4 total light become 

 darker in color, and decomposition takes place. 



5. Reduced light causes the death of oospores and sporelings when 

 planted more than 3 dm. below the surface of the water. 



6. Light is a controlling factor in determining the lower limit of 

 Fucus. 



