400 
the paraspores only arise in the tetraspore-bearing plants is probably connected 
with their number of chromosomes. Their nuclei are undoubtedly diploid, and it 
must be expected that they always give rise to tetraspore-bearing plants. It is in 
that respect interesting that in all the paraspore-producing species sexual individuals 
are either entirely wanting or extremely rare (Ceramium) in the Danish waters. And 
the fact that their development is in inverse proportion to that of the tetrasporangia 
is certainly the expression of a correlation similar to that existing in numerous 
Hepaticæ, Musci and many other plants between the sexual reproduction and the 
asexual propagation. 
7. The occurrence of sexual organs and tetrasporangia in the same plant 
has been ascertained in several species in the Danish waters. It is a particularly 
common appearance in Spermothamnion repens, where the sexual organs almost 
always occur together with sporangia. In Callithamnion tetragonum too the antheridia 
and the procarps occur frequently in the tetraspore-bearing plants. In 1864 and 1878 
Tuuret described a f. amphicarpa of C. corymbosum presenting the same combination 
but this form has not been observed in the Danish waters. In C. Furcellariæ I have 
once met with a procarp in a tetraspore-bearing plant, and in Antithamnion Plumula 
tetrasporangia were twice met with in a female plant. In Antithamnion boreale and 
Rhodochorton penicilliforme antheridia were detected, occurring in tetraspore-bearing 
plants, while female sex organs are still unknown. 
8. Occurrence of the various organs of reproduction in the Danish waters. 
Sexual organs have not been met with in Callithamnion Hookeri, Seirospora Griffith- 
siana, Plumaria elegans and Antithamnion cruciatum, while sexual plants of these 
species occur elsewhere. The three first-named species propagate in the Danish waters 
principally by paraspores, but tetraspores have been met with in all of them. In 
Antithamnion cruciatum sexual organs seem altogether to be a rare occurrence. 
Sexual plants of Spermothamnion repens occur only in the North Sea, the Skagerak, 
the Kattegat and the northern part ofthe Sound while the species in the inner waters 
only bears tetrasporangia or is sterile. In Ceramium diaphanum, C. strietum, C. Rosen- 
vingü, C. Boergesenii and Antithamnion Plumula the sexual plants are much rarer 
than the tetraspore-bearing ones. Of Callithamnion corymbosum only sterile plants 
have been met with in the inner parts of the area of the species (Sm, Su south 
of Hveen, Baltic). 
9. Vegetative propagation occurs in Rhodochorton Rothii, fragments of the 
erect shoots loosening and producing from the plane of detachment a downward 
growing filament which is able to fix the fragment as a cutting to a new substratum. 
Similar cuttings were observed in a culture of Seirospora Griffithsiana. 
