228 



p. 63) thai the characters pointed out by Foslie are not sufficient for generic di- 

 stinction but only for separation of sections beyond the genus. The roof of the 

 sporangia! conceptacles is frequently scarcely immersed, and it is often, particularly 

 in L. IcEvigatiim, convex within a feebly elevated border. 



7. Lithotliamnion polymorphum (L.) Aresch. 



J. E. Aresclioug in J. Agardh, Spec. II, pars 2, 1852, p. 524 ex parte; Rosanoff, Melobes., p. 99; Stromfelt, 

 Algveg. Isl., 188G, p. 19, pi. I, fig. 1—3 (sporangia); Foslie, Norw. Forms, p. 86, pi. 17, fig. 17—23 (f. 

 tuberculata, f. valida and t. papillata) ; Mme P. Lemoine, Structure, 1911, p. 87, pi. V fig. 2. 



Phymatolithon pohjmorphum (L.) Foslie, Syst. Survey, 1898, p. 4, Remai'ks, 1906, p. 75. 



Eleutherospora polymorpha (L.) Heydrich, Litli. HelgoL, 1900, p. 65, Taf. II, fig. 1 — 14. 



The species forms more or less irregular crusts extended over larger boulders, 

 of a thickness of up to 6 mm. As to the structure reference may be made to the 



taining starch grains at the ends of the cells but not in the middle were indeed 

 observed, but only as exceptions. Transversal fusions between the cells of the peri- 

 thallium occur here and there. 



The increase in thickness of the crust normally takes place by continued growth 

 of the perithallium, which may show several zones limited by horizontal, but some- 

 what irregularly running lines. In older crusts a more complex structure may be 

 found, the frond being composed of two or more crusts one over the other, each 

 with a particular hypothallium. This arises through cessation of growth in thick- 

 ness in certain parts of the perithallium, which become overgrown by new crusts 

 developing from other parts of the crust. This structure has been mentioned by 

 Mme Lemoine (Struct, p. 24 and 88, pi. V fig. 2), who appears to consider it as 



Fig. 145. 



Litliotluimnion pulfimorphnm. A. vertical section of frond 

 showing the hypothallium nnd the lower part of the peri- 

 thallium. B, vertical tlUiinents of another frond with nar- 

 rower cells. C, cells of perithallium with starch ^»rains. 350:1. 



papers of Foslie (1906) and Mme Le- 

 moine. The hypothallium is shown in 

 fig. 145 A. The cells of the perithallium 

 are somewhat variable in thickness, 4—7/^, 

 in some specimens proportionally narrow, 

 4 — 5 [/. (fig. 145 B). Mme Lemoine men- 

 tions as an interesting character that the 

 starch grains are single, very small and 

 grouped at the ends of the cells. This is, 

 however, not always so, for I found the 

 starch grains up to 3 /i in diameter, and 

 in some parts, frequently the greater part 

 of the crust, all the cells were filled with 

 starch grains, while they were totally 

 wanting in others, Particularly abund- 

 ant starch grains were found in the tissue 

 filling out the emptied conceptacles in , 

 the inner part of the crusts. Cells con- 



