III. Cryptonemiales. 



Fam. 4. Dumontiaceae. 

 Dumontia Lamour. 

 1. Dumoutiii iiicrassata (O. F. Miill.) Lamour. 



Laniouroiix, Essai. Mus. d'hist. nat. Paris 1813; Batters, Catalogue, 1902, p. 93. 

 Ulva iiicrassata O. Fr. Miiller, Flora Danica tab. 653, 1775. 



Ulua spoiigiformis O. Fr. Miiller, Flora Danica tab. 763 fig. 2, 1778(?). Fragment not determinable with 

 certainty. 



Ulva filiformis Hornemann, Flora Danica tab. 1480,2, 1813. 

 Gastridium fili forme Lyngbye, Hydr. p. 68 tab. 17. 



Gastridium filiforme var. intestiniformis Liebman, Flora Danica tab. 2457, 1845 = f. crispata Grev. 



Dumontia filiformis (Hornem.) Greville, Alg. Brit. p. 165 tab. 17 (cystocarp); Harvey, Fliyc. Brit. pi. 59 

 and 357 B; Naegeli, Die neueren Algensysteme 1847, p. 243 Taf. IX fig. 4—8 (structure of frond) ; J. Agardh, 

 Spec. II p. 249, III p. 257; Kiitzing, Tab. phyc. 16. Band Taf. 81 (transverse section of tetraspore- 

 bearing plant; Schmitz, Befr. Flor. 1883 p. 18,20, fig. 22 (carpogonial filament); Reinke, Algenflora 

 d. westl. Osts. p. 26; G. Brebner, On the Origin of the filamentous thallus of Duijiontia filiformis. 

 Journ. Linn. Soc. Bot. Vol. 30, 1895, p. 436; Kuckuck, figure of a young basal disc in Oltmanns' 

 Morph. I, p. 573; Okamura, Icones of Jap. Alg. Vol. I No. IV pi. 16 figs. 1 — 8, p. 65. 



The fronds arise from a crustaceous disc produced by tlie germinating spore. 

 A 5 days old plant is shown in fig. 74 A. It is not much larger than the tetraspore 

 from which it arose, but it is divided into a number of small cells and has become 

 a hemispherical body from the border of which short one- or two-celled filaments 

 proceed.^ A later stage is figured by Kuckuck (Oltmanns 1. c); a group of short- 

 celled filaments is here seen given off from the upper side of the disc, and it is 

 said that only one of these filaments serves to form the erect frond, some of the 

 others forming the bark on the base of it. The basal discs may be perennial (Reinke, 

 Brebner); they form large expansions on stones, Mytihis, Chondrus a. o. In sunny 

 localities they have a light violaceous colour and often show radial folding (in 

 a dried state), in greater depths they are darker, They are easily distinguishable 

 by their structure and by the occurrence of groups of short-celled filaments giving 

 rise to new erect fronds. As shown by Brebner (1. c.) the fronds may be endogenous 



' The germination of the tetraspores has quite recently' been described by Kvlin (Uber die Kei- 

 mung der Florideensporen. Arkiv for Botanik. Band 14. N:o 22. Stockholm 1917, p. 9). The author kept 

 the sporelings In culture during more than two months but did not obtain any production of erect 

 shoots. The sporelings produced after 10 days long unicellular hairs, but after addition of nitrate to 

 the culture no hairs were produced. 



20* 



