Howe: Phycological studies 515 



Plate 26. Ilalimeda discoidea 

 Photograph of a formalin -preserved specimen from Caesar's Creek, Florida {no. 

 2g64, 31 Mr 1904), natural size. 



Platk 27 



I. Halimeda tridcns. Photograph of a formalin-preserved fertile specimen from 

 Tallaboa, Porto Rico {no. 4424, 22 Mr 1906), natural size. 



2-4. Halimeda Tuna. Photograph of formalin-preserved fertile specimens from 

 Culebra Island, Porto Rico {no. 4201, 3 Mr 1906), natural size. 



Plate 28 

 I and 2. Ilalimeda Tuna 

 I and 2. Sporangiophores of apparently lateral origin from the central filaments 

 and formed without fusion ; these were from the flattened face of a segment. 



The figures are drawn from formalin-preserved material of our no. 4201 (Culebra 

 Island, Porto Rico) ; the magnification is 24 diameters. 



3-7. Halimeda tridens 



3. A cluster of three sporangiophores from the margin of a segment ; each is a 

 continuation of a filament of the central strand coherent with the adjacent filaments 

 near the point of emergence and anastomosing with them. 



4. A sporangiophore from the flattened face of a segment ; this is a direct con- 

 tinuation of a utricle (distal series) of the subcortical layer. 



5. Base of sporangiophore of origin similar to that shown in Figure 4. 



6 and 7. Bases of sporangiophores from the flattened faces of segments ; these 

 are direct continuations of the peripheral utricles ; in Figure 6 the sporangiophore forks 

 at the base, perhaps abortively. 



Figures 3-7 are drawn from formalin-preserved material of our no. 4424 (Talla- 

 boa, Porto Rico) ; all are magnified 24 diameters. 



8-26. Avrainvillea nigricans 



8. Portion of surface of the flabellum, with exserted sporangia. 

 9-13. Young sporangia in various stages of development. Near the middle of the 

 stipe in Figure 13 is indicated the position of the mucous or callose plug. 



14. A sporangium which has aborted and resumed vegetative growth. 



15. A nearly mature sporangium; the figure shows the mucous plug near the 

 base of the stipe and the usual relation of the sporangiophore to the vegetative 

 filaments. 



16. A young sporangium paired with an old and empty one. 



17. A sporangium with spores nearly formed. 



18. A pair of empty and shriveled sporangia, showing the wide erose or lacerate 

 opening at the apex of each and the mucous or callose thickening at the base of the 

 sporangiophore. 



19. A spore adhering to the mouth of an empty sporangium, where it has begun 

 its extra-sporangial development. 



20. A healed-over " stump " left by the decay of an old sporangiophore. 



21. A mature sporangium with four spores. A collection of granules at the apex 

 seems to indicate the area of the future rupture of the sporangium-wall. 



