502 Transactions of the Society. 



Sirodot (= Chantransia investiens Lenor.), the latter a fresh- 

 water species, in which the more or less branched thallus consists 

 of single rows of superposed cells. In Erythrotrichia Aresch., 

 generally included in this family on account of its red colour, the 

 structure is yet simpler, consisting of an unbranched filament of 

 single cells placed end to end ; but as the organs of reproduction 



branches, charaoierihtic of this genus, are due to local growth. The upper 

 cells are wedge-shaped, and the corticating cells a, a, first appear on the broadest 

 end of the wedge-shaped cells, thus causing the tip to curve. At some distance 

 behind the growing point the thin end of the wedge-shaped cells grows fastest, 

 and the corticating branches develope all round, pushing the stem back until 

 straight. X 300. 



Figs. 10 & 11. — CaUithamnion pobjspermum Ag. Showing the segmentation of 

 the apical cell by oblique septa in the main axis. The segmentation of the 

 branches is from the first by septa at right-angles to the axis of growth. X 300. 



Fig. 12. — Polysiphonia fastigiata Grev. Section of axial cells, showing 

 portions of protoplasm b, b, imprisoned between the primary layer a, a, and the 

 secondary layers c, c, c, c, of the cell-wall ; d, d, protoplasm of cells. X 000. 



Fig. 13. — Pohjsiphonia urceolata Grev. Surface view, illustrating the type of 

 stem composed of fascicles of cells of equal length, x 250. 



Fig. 14. — Transverse section of fig. 13, through a, 6, showing the axial and 

 four pericentral cells, x 250. 



Fig. 15. — Ceramium rubrum. Germinating spore, showing origin of adpressed 

 corticating branches a, a. x 300. 



Fig. 16. — Ceramium flabelligcrum J. Ag. Surface view, showing corticating 

 branches a, a ; 6, b, axial cells, x 250. 



Fig. 17. — Batrachospermum moniliforme Roth. Showing the basal portions of 

 two whorls of branches, which originate from the anterior end of axial cells a, a ; 

 b, b, free branches of whorls, the corticating branches are shown at c, c. The 

 portion represented is near the tip of the stem, and the adpressed branches are 

 as yet short, and few in number, x 300. 



Fig. 18. — Gloiosiphonia capillaris Carm. Vertical section, illustrating the typ8 

 of thallus composed of agglutinated branches. The axial cells are seen at a, 

 giving off whorls of branches at d, d, which become densely branched, and at the 

 tips composed of minute cells forming the " cortex " b. Some of the secondary 

 branches do not grow towards the circumference, but parallel to the axis, as shown 

 at c, c. x 250. 



Fig. 19. — Transverse section of fig. 18, through one of the whorls of branches ; 

 lettering same as in previous fig. X 250. 



Fig. 20. — Lenormandia linearis Harv. .Illustrating the development of a 

 flattened thallus from the cylindrical Polysiphonia type, due to local growth. In 

 the anical region the section is circular, and consists of an axial and pericentral 

 cells ; further back, as shown in the fig., the lateral wings a, a, are the result of 

 the continued growth and division of the pericentral cells, the anterioposterior 

 cells b, b, remain rudimentary. After Agardh, ' Florideernes Morphologi,' tab. 33, 

 fig- 17. 



Fig. 21. — Ptilota plumosa Ag. Showing the development of a flattened 

 thallus from the joining together of the " veins " which represent the outline of 

 a simpler filamentous form, by a membrane ; a axis, b lateral branches with pinnate 

 arrangement. In this species the membrane only forms a broad wing to each vein. 

 X 25. 



Fig. 22. — P. plumosa. Surface view of one of the lateral branches, showing 

 the axial row of cells a, from which all the other cells originate. X 250. 



Fig. 23. — Transverse section of fig. 22, showing the development of the wing 

 or membrane to be due to excessive growth and repeated division of the lateral 

 pericentral cells. X 250. 



Fig. 24. — Delesseria ( Wormskioldia) sanguinea Lamour. Apical part of one of 

 the leaf-like portions of the thallus, showing the main axis a, with pinnately 



