154 Wilson. — On Spore Formation and Nuclear 
with the Hepaticae and Ferns, is further strengthened by the description 
of the process in Mnium hornum . Their further surprising statements-, 
that a second reduction takes place on the last division of the spermato* 
genic cells, and that at fertilization the egg fuses with two spermatozoids, 
and with the Ventral canal cell, will need abundant confirmation before 
they can be accepted. 
This is especially the case, as Dr. Arens, who has recently investigated 
the spermatogenesis of both P oly trichum juniperinum and Mnium hornum\ 
finds that in each case the development is normal. At present no state-* 
ments can be made with regard to the spermatogenesis and fertilization of 
Mnium hornum , but the investigation of this plant is being continued, 
and it is hoped that results will be forthcoming within a short period. 
Summary. 
1. Fertilization takes place in Mnium hornum during May; the 
single-celled archesporium can be recognized early in the following 
January. Spore formation and chromosome reduction are completed 
about the middle of April. 
2. The resting nucleus, both in vegetative and reproductive cells, is 
characterized by the presence of a very large deeply-staining nucleolus ; 
the nuclear reticulum is very fine, and contains little or no chromatin. 
3. Each original cell of the archesporium gives rise to 8, 16, or 32 
spore-mother-cells. On the approach of somatic division the nucleus 
becomes more granular, and broad band-like masses of chromatin are 
differentiated ; the nucleolus gradually loses its staining power and dis- 
appears. By contraction of the chromatin masses the spireme is formed, 
and in this no sign of longitudinal fission could be discovered. 
4. The spireme divides transversely into twelve chromosomes of 
approximately equal size, and these become arranged on the equatorial 
plate of the spindle. No centrosomes or polar radiations are present. 
5. The chromosomes split longitudinally and the halves retreat towards 
the poles. The telophase follows the usual course ; several nucleoli are at 
first formed, but later these fuse into one. 
6. The wall dividing the daughter-cells is laid down as usual at the 
equatorial plate. 
7. There is a period of rest after the formation of the spore-mother*- 
cells ; the resting nucleus resembles that of the premeiotic cells, but contains 
slightly more chromatin. While in the resting state a body is budded 
off from the nucleolus, and this persists until after the first synapsis, and 
then disappears, 
8. The spireme is gradually differentiated from the nuclear reticulum, 
forms a definite network, and then gives rise to the first contraction 
figure. In this there is no lateral approximation of individual filaments. 
