238 



cells, as the occurrence and frequency of these cells seems to depend to a great 

 extent upon external conditions. I therefore attach but little importance to the fact 

 that such have not hitherto been found in two of the species mentioned below 

 (M. minutiila and microspora) as it must be considered highly probably that they 

 will be found on further investigation of a greater number of specimens. More- 

 over, hair-cells are found in M. Lejolisii, noted by Foslie under the genus Hetero- 

 derma (see fig. 156). On the otlier hand, I could well imagine that it may later on 

 be found justifiable to distinguish between those species in which tlae trichocytes 

 are terminal in the horizontal cell filaments, as in M. farinosa, for instance, and the 

 other, doubtless far more numerous species in whicli they are intercalary. Another 

 vegetative character which might be thought to furnish grounds for generic distinc- 

 tion, is the lack of cortical cells shown below in the case of M. microspora. This 

 point, however, still needs further investigation. As regards tlie cortical cells, it may 

 also here be noted that in M. trichostoma, several of tliese were found above one 

 anotlier, cut off successively by the same frond cell. 



Where the frond consists of more than one cell-layer, there is often but slight 

 difference between the basal layer (liypothallium) and the upright cell filaments 

 proceeding therefrom (perithallium). Thus the walls forming the boundary between 

 these two tissues often lie at different heiglits, as for instance in M. microspora 

 (figs. 176—179) and M. trichostoma (174 175). 



The number of spores in the sporangia is in most of the present species con- 

 stant, fn four species, 4 spores were found, in M. subplana a constant 2. fn M. mi- 

 nutiila only specimens with 4 spores were found, whereas Fosi.ik gives 2, and in 

 M. Fosliei some conceptacles were found with 4, others witli 2 spores in tlie spor- 

 angia. — A small stalk-cell under the sporangium was found in M. subplana. 



With regard to the antlieridia, M. Lejolisii was found to difTer from the other 

 species in liaving the sperinatangia formed at the end of long sterigmata, as first 

 shown by Mrs. Webeh-van Bosse. In the other species, the spermaiangia are elonga- 

 ted cells, situate on tlie flat bottom of tlie antheridia-conceptacles. The orifice of 

 the antheridia-conceptacles was in four of the present species often found drawn 

 out into a spout, as first shown by Mrs. Weber-van Bosse in the case of M. Lejolisii. 

 This is, however, not a constant character, as it may frequently be lacking in all 

 the species concerned. 



The carpospores are in all the cases investigated formed only in the periphery 

 of the coiiceptacle, at the margin of the flat disc-cell. 



1. Melobesia Lejolisii Rosanoff, 



Rosanoff, Rech. anat., 1866, p. 62, pi. I fig. 1—1,3, pi. Vll fig. 9 — 11; Areschoug, Observ. phycolog. Part. 

 Ill, 1875, p. 3; Hauck, Meeresalg., p. 264; A. Weber-van Bosse, Rijdrage tot de Algenflora van Neder- 

 land, Nederl. kruidk. archief. 2. Ser. 4. deal 4e stuk, Nijmegen 1886, p. 36.'); ead. in Hauck et Richter, 

 Phj'kotheka imivers. No. 163; Foslie, Remarks, 1!)05 1906) p. 102 f. typica); Mine P. Lemoine, Struct., 

 p. 180, fig. 103; ead.. Calcareous Algae in Report on the Danish Oceanogr. Exped. 1908—10 to the 

 Mediterranean etc. Vol. II, 191.'), p. 19. 



I 



