the cells, finally resulting in a fusion of the nuclei themselves. If this were so, 
then the fusion of the nuclei would be of no particular importance in itself, but 
merely a consequence of the cell-fusion. Such supposed co-operation of the nuclei 
in effecting the fusion of cells is, however, purely hypothetical: I have not with 
certainty observed the nuclei immediately prior to commencement of the fusions, 
and it must be admitted that certain cases where cell fusions took place between 
four cells (fig. 127 D) do not tend to support the theory. Fusion of nuclei in vegeta- 
tive cells of higher plants has recently been observed in several cases, where cells 
have, for some reason or other, proved to contain more than one nucleus (cf. for 
instance Schürhoff, Kernverschmelzungen in der Sprossspitze von Asparagus offici- 
nalis. Flora, N. F. 8. Bd. 1916, p. 55). 
The cells always contain, fusions apart, a single nucleus. The only exception 
is the female plant of Corallina officinalis, where the cells of the central tissue con- 
tained from two to four nuclei. The chromatophores are small, disc-shaped; there 
is often a rather small number in each cell (figs. 130, 143 E; comp. Pilger 1. c. p. 253). 
Starch-grains occur in all the species. They are often very numerous, parti- 
cularly in the older tissues. Mme LEMOINE distinguishes between single and com- 
pound (coalescents) starch grains. According to my observations, this distinction 
appears to depend exclusively on whether the cells are more or less densely filled 
with starch grains, in the first case the grains may be applanated on the faces 
where they meet, as also stated by PiLGER (l. c. p. 254), but they are not really 
connate. In Lithothamnion glaciale var. Granii, which is said by Mme LEMOINE to 
possess compound starch grains, I found distinct single grains (fig. 128). The starch- 
grains frequently contain a small air-bubble in the centre in the preparations from 
dried specimens (comp. figs. 130 B, 143 F, 174). 
The well known transversal limiting lines which undoubtedly indicate periods 
of stand-still in the growth occur in all the species of Lithothamnion, except those - 
with thin crust, but they are also met with in Lithophyllum orbiculatum (fig. 180 A), 
whereas Mme Lemoine did not find them in any species of this genus (I. c. p. 28). 
As shown by this author they are very intensely stained by hæmatoxyline; they 
may pass between the cells, coinciding with the middle-lamella, but more frequently 
they meet the longitudinal walls of the cells without bending under them (figs. 
136, 138, 143, 144, 145). Mme Lemoine describes further alternating zones with 
varying power of staining with hæmatoxyline. Such zones, not limited by a blue 
line, were met with in Lithophyllum norvegicum where the ordinary limiting lines 
were otherwise also present (fig, 143 B, C). 
In some genera (Melobesia, Lithophyllum, Corallina) unicellular, hyaline hairs 
occur. They resemble those occurring in numerous other Florideæ (com. L. KOLDERUP 
ROSENVINGE, Remarks on hyal. unic. hairs; Biolog. Arb. tilegn. E. Warming, 1911, 
p. 203) but differ, however, in not being limited from the cell producing them by 
a transversal wall. The hair-producing cells have been long known in the species 
of Melobesia, particularly M. farinosa, where they were given the name of heterocysts 
