PLATE I. 



(Frontispiece.) 



FIG-. PAGE 



1. Sargassum vulgare 36 



1 a, air-vessel. 



1 b, spore-receptacles. 



2. Halidrys siliquosa 38 



2 a, section of receptacle, showing spores, mag- 



nified. 



3. Pycnophycus tuberculatus 41 



3 a, section of receptacle, showing spores, mag- 



nified. 



4. Leathesia tuberiformis 69 



4 a, filaments with spores. 



