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1903 | MITOSIS IN PELLIA 29 
published a more extended paper dealing with spore-formation 
and nuclear division in Fossombronia, Pellia, Conocephalus, and 
several other forms. In most of these forms, centrosomes were 
observed to play an important réle in mitosis. The occurrence 
of centrosomes in Pellia was confirmed by Strasburger (33) from 
Farmer’s own preparations. 
In 1899 Davis (6) studied the spore mother-cell of Anthoce- 
ros. In the two divisions by which the tetrad is formed from 
the mother-cell, the spindle during the metaphase is flattened 
at the poles and entirely lacks bodies which might be inter- 
preted as centrosomes or centrospheres. The spore walls are 
described as being formed independently of the spindle. 
The following year Van Hook (38), with more favorable 
material, confirmed Davis’s statement that there are no centrosomes 
in the spore mother-cells of Anthoceros, but found the spindle 
functioning as in Lilium in the formation of spore walls. In 
the same paper Van Hook figured and described definite centro- 
somes in the vegetative cells of the gametophyte of Marchantia. 
In 1901 Davis (7) made a detailed study of mitosis in various 
phases of the life-history of Pellia. Centrospheres were found 
during the early divisions in the germinating spore, but could 
not be identified in the sporophyte or in later stages of the 
development of the gametophyte. 
At this time it hardly seems desirable to make a more 
extended résumé of the literature, since it is still too incomplete 
and indefinite to warrant generalizations. In presenting our own 
results, we shall occasionally refer to the preceding papers and 
also to papers dealing with mitosis in other groups. 
MATERIAL AND METHODS. 
Most of the material for this work was collected near Bonn 
in Melbthal and in the Siebengebirge. Early in October the 
Spore mother-cells of Pellia are already quite deeply lobed, and 
occasionally a sporogonium is found in which the spores are 
already formed. By the middle of November nearly all of the 
Spore mother-cells have divided and many of the spores have 
8erminated. The winter of 1901-2, in the Rhine Province, was a 
