Howe : Phycological studies 585 



16. The branch at the right represents a later stage in the development of the 

 cortex, X 55- 



17. Cross-section of stipe, X 4- 



18. Cortical region of stipe in cross-section, X I 5°- Drawn from a microtome 

 section 20 p. in thickness. 



19. A stage in the differentiation of the cortical filaments later than that shown in 

 figure 16, X 55- 



20. Final form of cortical filaments of capitulum, X l 5°- 



Figures 11-20 are drawn from formalin -preserved material of the type, no. 4079 

 (Georgetown, Great Exuma, Bahamas). 



Plate 27. Sarcomenia filamentosa 



Photograph of dried specimen (no. 2S44, type — , Cape Florida, 29 Mr 1904, M. 

 A. H. ) attached to Sargassum, natural size. 



Plate 28. Dudresnaya crassa 



Photograph of dried specimen (no. j/j, type — , Castle Harbor, Bermuda, 6 Jl 

 1900, M. A. H.), natural size. 



Plate 29 



I-I I . Sarcomenia filamentosa 



1. Apex of polysiphonous branchlet, ventral view, showing apical cell and origin 

 of the paired marginal cells and of the monosiphonous filaments, X I 93- 



2. Older part of branchlet, dorsal view, X x 93- 



3 and 4. Cross sections of uncorticated branchlets, ventral side downward, X I 93- 



5. Apical portion of uncorticated branchlet, with the unifarious monosiphonous 

 filaments, X4^- 



6. Branchlet viewed from margin, showing bases of the monosiphonous filaments, 



Xi93- 



7. Part of an older branch, ventral view, showing origin of polysiphonous branch- 

 let (really from axial siphon), X 44- Marginal cells at somewhat regular intervals are 

 enlarged and protuberant (potentially rhizoids). The monosiphonous filaments have 

 here disappeared, but the cell cut off from the anterior end of the ventral siphon marks 

 their former position in each thallus-segment. Small intercalary cells, originating 

 chiefly from the pericentral siphons, constitute the beginning of the cortex. 



8. A similar branch, dorsal view, X44- The rhizoids are here growing out. 



9. Surface view near the base of one of the largest stems seen, showing cortical 

 cells, X 4°- 



io. Cross-section of a similar main stem X 44- 



11. Cross-section of an ordinary main axis in the basal third of the plant, X 44- 

 Figures 9 and 10 are drawn from our no. 2860 ; figures 1-9, and II are from the 



type material, no. 2844 (Cape Florida). 



12-26. Dudresnaya crassa 



12. Outer portion of peripheral filament. 

 13-15. Carpogonial branches. 



16 and 17. Auxiliary-cell branches; auxiliary-cell occupying middle of enlarged 

 portion, lying between two much larger cells. 



