328 
Notes. 
show varying degrees of specialization, for which the mycorhizic habit and the habitat 
give a reasonable explanation. Moreover, the anatomical fact that the leaf-trace in 
0 . pendulum and 0 . simplex is composed of several strands at the base in place of one 
(1. c., p. 21) supports the opinion that they are not primitive types of the genus. 
Lastly, the fact that the vestigial lamina is clearly seen in some of Prof. Rosenstock’s 
specimens would be less easily harmonized with the view of 0 . simplex as a primi- 
tive form than it would with the theory of reduction above expressed. 
F. O. BOWER. 
Glasgow, February , 1908. 
PRELIMINARY NOTE ON NUCLEAR DIVISION IN MNIUM HORNUM. 
— Nuclear division in the Mosses has up to the present time received but little 
attention. Beer 1 found four chromosomes in the dividing spore-mother-cells of 
Funaria hygrometrica, but stated later 2 that the number in this plant and in 
several other species, including Mnium hornum , was far greater. He also refers to 
the compound nucleoli in the spermatogenic cells of A trichum undulatum. 
The premeiotic divisions have been studied in the developing archesporium of 
Mnium hornum. The resting nucleus is made up of a fine homogeneous network 
and a single large centrally placed nucleolus. The latter contains almost the whole 
of the chromatin and by its persistence dominates the early stages of the division. At 
its first appearance the spireme consists of broad band- like masses of chromatin 
which are found especially at the periphery of the nucleus ; by the further contrac- 
tion of the chromatin a thin, thread-like spireme is formed. At this stage the nucle- 
olus stains much less deeply, loses its sharp outline, and, a little later, breaks up and 
disappears. Twelve chromosomes are formed by the breaking up of the spireme, 
and these become arranged on the equator of the spindle showing the slender, hook-like 
form characteristic of the somatic divisions. The diaster originates in the usual 
manner by the splitting of the chromosomes, and during the anaphase and telophase 
the latter pass through changes resembling those described in the prophase. 
A short period of rest elapses after the final division of the archesporial cells. 
The resting nucleus of the spore mother-cells shows the characteristic nucleolus and 
a somewhat coarser reticulum than that of the premeiotic cells. The closely coiled 
spireme arises by an increase of the chromatin in the nuclear reticulum. Contraction 
of the thread then takes place and results in a definite synapsis. On emerging, the 
thread thickens at the expense of the nucleolus which gradually disappears. The 
spireme divides up into six chromosomes which show the O- and the irregular X- 
forms characteristic of the reduction division. After separation the chromosomes 
pass outwards to form the daughter-nuclei. These do not enter into a completely 
resting condition, but quickly undergo the homotype division. This resembles 
the premeiotic divisions in its chief features. A full description of the divisions with 
figures will shortly be published. 
M. WILSON. 
Royal College of Science, S. Kensington. 
1 New Phytologist, vol. ii, 1903, p. 166. 
2 On the Development of the Spores of Riccia glauca. Annals of Botany, vol. xx, 1906, p. 278, 
footnote. 
