el 
General Remarks on the Danish Species of the Gigartinales Rhodymeniales 
and Nemastomatales. 
Reproduction, Alternation of Generations. 
Of the 18 species of these groups mentioned above, 11 only have the typical 
alternation of generations peculiar to the Florideæ. In one of these species the 
two generations do not occur simultaneously. As shown by Srurcn, the sporophytic 
individuals of Harveyella mirabilis occur, at the British shores, in early spring, 
whereas the cystocarps are only met with in winter (December, January). In the 
Danish waters and at the west coast of Sweden the behaviour of this species is 
similar, for the cystocarps have only been observed in December and January, and 
the tetrasporangia most frequently occur in April to June, in individuals growing 
on branches and branchlets of Rhodomela produced in winter and thrown off in 
summer. The tetrasporangia are thus developed a little later in the Danish than 
in the British waters, and latest in the inner Danish waters. It must, therefore, be 
concluded, that two short-living generations, a sexual generation and a tetraspore- 
generation, succeeding each other, are produced in the course of one year. Aberra- 
tions from this scheme may, however, sometimes occur; e. g. individuals with the 
two kinds of sex organs and others with tetrasporangia were once found growing 
simultaneously on the same host plant in October, probably owing to special external 
conditions. On the other hand, the life-history of the species is different in the 
Arctic Sea, for it has only been found with sex organs and cystocarps in Scoresby 
Sound (East Greenland), whereas tetrasporangia were not met with at all, and it 
seems, therefore, that the sexual generation only is developed in the Arctic Sea. 
The behaviour of Harveyella mirabilis at the shores of Northern Europe is a 
rare example of seasonal alternation of generations. SVEDELIUS has first used this term 
for the life history of Ceramium corticatulum in the Baltic. This species has there 
an ephemeric gametophyte generation in late summer and a winter generation of 
tetrasporic plants, and SvEDELIUS points out that a similar seasonal alternation of 
generations has formerly been ascertained in Chantransia efflorescens and in Harveyella 
mirabilis. As to the former it must be admitted that no exact proof has been 
given of the assumption that Rhodochorton chantransioides is the sporophytic 
generation of Chantransia efflorescens, as maintained by Kyrın® and myself”, and 
that the life-history of the species, therefore, needs further experimental and cyto- 
logical investigation. 
1 N. SVEDELIUS, The seasonal alternation of generations of Ceramium corticatulum in the Baltic. 
N.A. reg. soc. sc. Upsal. Upsala 1927. — G. SJÖSTEDT, Revision of some dubious Swedish Ceramium types, 
their classification and ecology. Lunds Univ. Arsskrift, N. F. Avd. 2. Bd. 23, Nr. 12. 1928. — N. SVEDELIUS, 
The seasonal Alternation of Generations of Ceramium corticatulum. Svensk Botanisk Tidskrift, Bd. 23, 1929. 
? H. Kyrın, Zur Kenntnis einiger schwedischen Chantransia-Arten. Botan. Studier tillagnade F. R 
Kjellman. Uppsala 1906, p. 113. 
® L. KOLDERUP ROSENVINGE, Mar. Alg. Denm. Part. I, 1909, p. 137. 
