Division in Mninm hormim. 
147 
sets in, and each protoplast separates slightly from the wall and lies free 
in the cavity. As a general rule, nuclear division takes place simultaneously 
in the whole of the spore-mother-cells of the sporogonium, but a few 
exceptional cases have been discovered. In these, although the majority 
of the nuclei were in the same state, some few were found in the immediately 
preceding or following stages ; in all cases, cells of the same group divide 
simultaneously. 
The nuclei resemble those already described in the premeiotic resting 
cells, but in the spore-mother-cells the nuclear reticulum is, on the whole, 
coarser, and the chromatin is slightly more abundant (Fig. 14). In most of 
the nuclei, in addition to the nucleolus, a small deeply-staining rounded 
body is present. This varies in position, being sometimes situated in contact 
with the nucleolus, but generally about equidistant between the latter and 
the nuclear membrane (Figs. 14 and 17). A careful examination leads to 
the conclusion that this body arises from the nucleolus by a process of 
budding (Fig. 15), gradually increases in size, and is ultimately set free 
(Fig. 16). This structure is constantly found in preparations which have 
been fixed with Flemming’s solution, but it is absent from those previously 
treated with acetic alcohol. This fact confirms the view previously stated 
(p. 144), that by the use of the latter reagent some of the nuclear material 
is actually lost. 
In the spermatogenesis of Marchantia polymorpha , Ikeno ( 19 ) has 
described the formation of a similar body ; here, after its constriction 
from the nucleolus, it passes out through the nuclear membrane into the 
cytoplasm, and there, by division, gives rise to the two centrosomes. An 
examination of the spermatogenic cells of Mnium hornum reveals the 
presence of a similar structure with a like origin, but its ultimate fate has 
not yet been determined. In the spore-mother-cells of Mnium , the body in 
question certainly does not pass into the cytoplasm, and it can still be 
distinguished within the nucleus during the earlier stages of division. 
Gates ( 12 , p. 6) has figured a similar body in the heterotype division of 
Oenothera rubrinerms. He states that a large nucleolus and several smaller 
ones are present in the resting sporogenous cells, and that, as division 
approaches, fusion takes place until generally one large nucleolus and one 
smaller one remain; these persist during synapsis and diakinesis. Miss 
Nichols ( 22 ) has described a budding of the nucleolus in the pollen-mother* 
cells of Sarracenia , but this is interpreted as a fusion by Gates ( 12 , p, 6, 
footnote). Cardiff ( 7 ) has figured a similar budding in the pollen-mother- 
cell of Acer platanoides. In the case of Mnium , there can be no question of 
fusion, since only one of these bodies is present. 
The first sign of division is seen in nuclei which exhibit a coarser 
reticulum and more abundant chromatin (Fig. 17). The remarks made 
during the description of the early prophase of the premeiotic division (see 
