280 
mentioned on p. 210, this genus is characterised by the fact that the cells in the 
upright filaments, of which the frond (the perithallium) is composed, are connected 
by transverse pits, the origin of which must be of a secondary nature. I have not, 
however, been able to follow their development, and particularly did not succeed 
in ascertaining the co-operation of the nuclei in their formation. In the remaining 
members of the family of Corallinaceæ, on the other hand, there is a different method 
by which the cells in various filaments may.enter into direct communication one 
with another, to wit, by dissolution of the separating wall, whereby an open con- 
nection is established between the cells. This feature has already been referred to 
above (p. 210) where it was also pointed out that more than two cells may fuse 
together, and that the cell-fusions may involve fusion of the nuclei (cf. figs. 136, 139, 
156 and many others), Only in two of the Danish Corallinaceæ have the fusions 
hitherto not been shown (Melobesia minutula and Choreonema Thuretii). 
Entirely similar cell-fusions were demonstrated in various Squamariaceæ, viz, 
Cruoriopsis danica (p. 185 fig. 107), Cruoriopsis gracilis (p. 188 fig. 111), Rhododermis 
elegans (p. 198 fig. 118) and Rhododermis Georgii (p. 199 fig. 119). In Hildenbrandia, 
on the other hand, they were not found. 
That cell-fusions are important as facilitating connection between cells and 
cell-filaments not directly in communication by plasma-continuity can hardly be 
doubted. We find them also particularly numerous in the “roof” above the con- 
ceptacle lin the Corallinacez, i. e. between cells whose indirect connection below 
has been interrupted by the formation of the conceptacle. Comparison with Hilden- 
brandia, which lacks cell fusions, supports this view, as the roof of a conceptacle, 
which grows in extent through the continued sporangia formation, consists of dead 
and more or less disorganised cells, save at the margin, undoubtedly cwing to the 
fact that the connections below have been interrupted, and those to the sides are 
wanting (cf. p: 204 and figs. 125, 126.). 
3. Alternation of generations and alternation of nuclear phases. As we know, 
there has in several Floridee been shown to exist a regular alternation between a 
haplophase, consisting of the sexual generation, and a diplophase, consisting of two 
generations, viz; the cystocarp or gonimoblast, and the tetraspore-bearing plant’). 
A like course of development must be presumed to take place in all Florideæ with 
normal fertilisation, and having tetrasporangia. SVEDELIUS has called these Florideæ 
diplobiontic, in contrast to the haplobiontic, which lack tetraspores, and in which 
the chromosome reduction takes place by division of the zygote nucleus”). Here 
then, we have but two generations, the sexed plant and the cystocarpium, both 
y Comp. H. Kyrın, Die Entwick. u. syst. Stell. von Bonnemaisonia asparagoides etc. Zeitschr. £ 
Botanik, 8. Jahrg., 1916, p. 570. — J. Buper. Zur Frage des Generationswechsels im Pflanzenreiche. Ber. 
deut. bot. Ges. Bd. 34. 1916, Heft 8. — O. Renner, Zur Terminologie des pflanzlichen Generationswech- 
sels. Biolog. Centralblatt. Bd. 36, 1916, p. 337. 
*) N. Sveperius, Zytolog.-entwickelungsgesch. Stud. über Scinaia furcellata. N. Acta reg. soc. sc. 
Upsal. Ser. IV. vol. 4 no. 4. Upsala 1915, p. 22. 
