146 Wilson —On Spore Formation and Nuclear 
tained. At the next stage the chromosomes have become arranged on the 
equatorial plate (Fig. 8), but even now the spindle is not strongly marked, 
although the individual fibres can be distinguished ; the latter converge 
towards the poles, but no signs of centrosomes or of polar radiations were 
seen. The number of chromosomes can now be ascertained, and in all cases 
twelve are found to be present. They take the form of somewhat elongated 
sharply-bent rods with the hook-like arm lying at the equatorial plate, and, 
as far as can be judged, they are all of equal size. The number is most 
clearly shown in polar views (Fig. 9), where each chromosome is generally 
seen as a dumbbell-shaped structure, consisting of two clearly marked 
circular portions, united by a less distinct band. This appearance is given 
by the two arms of the chromosome in optical transverse section, while 
the connecting portion is dimly seen at a slightly different level. Up to 
this time twelve is the only number of chromosomes recorded in cytological 
examinations of the diploid generation in the Muscineae (Leeuwen-Reijnvaan, 
20 and 21), and this agrees with the number found in the present investigation. 
Longitudinal splitting of the chromosomes takes place on the equatorial 
plate, and the resulting halves retreat to the poles forming the usual 
diaster (Figs. 10 and 1 1). The retreating chromosomes are of the character- 
istic V-shape, and a polar view at this stage allows the number to be 
easily counted. Each chromosome is seen as two small dots, since the 
two arms of the V are seen in optical transverse section. On reaching the 
poles the chromosomes lose their sharp outline and become fused together, 
forming an irregularly-shaped mass of chromatin. This gradually loses its 
staining capacity, and, at the same time, several rounded nucleoli appear. 
The nuclear membrane becomes evident in each of the daughter-nuclei, 
which at first possess a flattened surface on the side towards the centre of 
the spindle (Fig. 12). Later on the nucleoli decrease in number, and 
ultimately one is produced by general fusion. The nucleus takes on a 
rounded form, finally becoming spherical or ellipsoidal (Fig. 13) ; during the 
telophase numerous darkly-staining masses of material are found in the 
cytoplasm. 
During the anaphase the spindle broadens out towards the poles and 
becomes very obvious, the new cell wall is laid down at the equatorial 
plate, and can first be distinguished as a fine granular deposit, extending 
across the spindle (Fig. 11). At the telophase the wall has become more 
obvious, and extends completely across the cell. 
T 7 ' S' l( - • •/ < 
V G The Meiotic Divisions. 
After the final divisions in the archesporial tissue have taken place the 
colls pass into a resting condition which continues for some time — as far as 
dotild be judged, from seven to ten days. Growth takes place and the cells 
increase considerably in size ; after a time, contraction of the protoplasm 
