609 
The reproduction of Phyllophora Brodie@i and Ahnfellia plicata exhibits instances 
of a much reduced alternation of generations. In Phyllophora Brodiwi it has been 
shown that the globular bodies, formerly usually considered as a parasite of the 
genus Actinococcus, are much reduced tetrasporophytes of Phyllophora Brodiei. The 
fronds of this species are all sexual plants usually bearing antheridia and procarps 
in the same individual. A fertilization process was not seen by the author, but 
observations of H. CLAUSSEN and Kyrın suggest that a fertilization and a transfer 
of a sporogenous nucleus to the auxiliary cell really take place. The auxiliary cell 
gives off protuberances which do not become gonimoblast filaments but grow out 
as intercellular cell-filaments which finally give rise to the nemathecial bodies 
forming cushions outside the surface of the frond. The carposporophyte is abandoned, 
and in its place a tetrasporophyte is developed. The intramatrical cell-filaments 
growing out from the auxiliary cell represent the much reduced vegetative part of 
the tetrasporophyte. 
Ahnfeltia plicata is a still more reduced type. Sex organs, fertilization process 
and cystocarps are wanting. The only organs of reproduction are the nemathecia, 
which produce monospores in the end-cells of the nemathecial filaments. In the 
young nemathecia small groups of generative cells appear which give rise to 
horizontal cell-rows and to secondary nemathecial cell-rows the end-cells of which 
develop into monosporangia. The groups of generative cells are considered as reduced 
procarps. These cells or some of them grow out into cell-rows partly in a horizontal, 
partly in a vertical direction, the latter forming secondary nemathecial filaments 
producing monospores in the end-cells. The whole complex of cell-filaments produced 
from the generative cells is considered as corresponding to the sporophytic phase 
of the typical diplobiontic Florideæ, although it arises without any fertilization 
process from the Ahnfeltia plant. The nemathecium of Ahnfeltia can be compared 
with that of Phyllophora Brodiei, and the monosporangia of the former with the 
tetrasporangia of the latter. The monosporangia can be interpreted as reduced 
tetrasporangia which have failed to be divided, in good accordance with the absence 
of a reduction division. 
Loose Forms of normally Attached Species. 
The fronds of a comparatively great number of the species treated in the fourth 
part of this work are able to maintain life for a shorter or longer time after having 
been disengaged from their support. When living long in a loose condition, the 
fronds are always sterile. In stormy weather numerous fronds of Algæ are torn 
away from their substratum. Many of them are washed ashore but a great number 
are carried by the currents to localities often situated far away from the spot where 
they were growing and where the external conditions may be rather different from 
those in their original growing place. The annual species and others with a soft 
consistency of the frond die shortly after having been loosened; those with a more 
solid structure are able to keep alive for some length of time. In the Danish waters 
D. K. D. Vidensk. Selsk. Skr.,7. Række, naturvidensk. og mathem. Afd., VII, 4. 78 
