142 Wilson. — On Spore Formation arid Nuclear 
hornum , but only gives a complete account of the first species. In this the 
nuclei of the cells of the young antheridium contain a very large, extremely 
deeply staining nucleolus : a few small grains of chromatin are embedded 
in the extra-nucleolar material, which otherwise exhibits no structure. 
He therefore concludes that the nucleolus contains the whole of the 
chromatic material. Eight chromosomes appeared at the metaphase of 
division. No centrosomes were found until the final division of the 
spermatogenic cells. Mnium hornum was found to be almost similar in 
structure, and in this not more than eight chromosomes appear during 
division. In a summary of this work, published later in the Botanisches 
Centralblatt, the number of chromosomes is corrected by the writer’s 
authority, and is given as six (2, p. 61 1, footnote). 
The most complete description of nuclear division in the Muscineae 
yet given is that of Drs. J. and W. van Leeuwen-Reijnvaan (20 and 21 ). 
They have examined four species of Polytrichum (P. piliferum , juni- 
perinum , for mo sum and commune ), but were unable to find the reduction 
divisions. A few divisions in the cells of the sporogenous layer are 
described, while more numerous divisions were found in the epidermis and 
parenchymatous tissue of the sporogonium. The chromosomes are 
described as very small and rod-like ; twelve appear during the division, 
and this number was found in all the species examined. No centrosomes 
were seen during the process. During spermatogenesis numerous dividing 
cells were found in the young antheridium. Immediately before division 
a small body is cut off from the nucleolus ; this passes into the cytoplasm, 
elongates, and then divides, giving rise to two centrospheres, which are 
later found at the poles of the spindle. Six chromosomes appear, and these 
show considerable differences in size ; two are small, two intermediate, and 
two large, and thus three distinct pairs can be distinguished. The authors 
therefore conclude, by analogy with Liverworts and Ferns, that a reduction 
in number of chromosomes has taken place on spore formation. At the 
last division of the spermatogenic cells the two chromosomes of each pair 
fuse laterally, and at the metaphase the three masses thus produced divide 
longitudinally, and three entire chromosomes pass to each pole of the 
spindle. In this way a second reduction in number of chromosomes is 
brought about. A similar second reduction is considered to take place 
during the development of the egg cell. At fertilization the ovum fuses 
with two spermatozoids and with the ventral canal cell, and in this way the 
original number of chromosomes is regained in the fertilized egg. 
Methods. 
Flemming’s Strong and Weak Mixtures, acetic alcohol (absolute 
alcohol two parts, glacial acetic acid one part), and Flemming’s Strong 
Mixture diluted with an equal quantity of water, were used as fixing 
