212 



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 efTecting 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 SchiirhofF, 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 (1. 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 ii, 143 F. 174). 



The well known transversal limiting lines which undoubtedly indicate periods 

 of stand-still in the growth occur in all Ihe species of Lithothamnion, except those 

 with thin crust, but they are also met with in Lithophijllum orbiculatum (fig. 180 A), 

 whereas Mme Lemoine did not find them in any species of this genus (1. c. p. 28). 

 As shown by this author they are very intensely stained by hsematoxyline; 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 hsematoxyline. Such zones, not limited by a blue 

 line, were met with in Lithophijllum norvegicum where llie ordinary limiting lines 

 were otherwise also present (fig, 143 B, C). 



In some genera (Melobesia, Lithophijllum, Corallina) unicellular, hyaline hairs 

 occur. They resemble those occurring in numerous other Floridese (com. L. Kolderup 

 Rosen vinge, 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 tlie species 

 of Melobesia, particularly M. farinosa, where they were given the name of heterocysts 



