Black. — The Morphology of Riccia Frostii , A test. 519 
of centrospheres in Anthoceros spore mother-cells. In a later paper on 
Pellia , Davis ( 13 ) finds no centrospheres in the spore mother-cell, but in 
the germinating spore a centrosphere and an aster are observed. Chamber- 
lain (11) finds centrospheres in the first mitosis of the germinating spore of 
Pellia. Moore (35) finds in P allavicinia, that while the prophase resembles 
the four-poled spindle of Farmer, it cannot be interpreted as such, because 
it is followed by a well-organized bipolar spindle without centrospheres. 
Garber describes the sporophyte spindle of R icciocarpus natans with 
prominent asters, but no centrosomes. Lewis for the same form finds 
neither centrosome nor centrosphere in the spore mother-cell divisions. 
Beer ( 5 ), in Riccia glanca , finds the resting nucleus of the spore mother- 
cell with a large, deeply staining nucleolus and a number of more faintly 
staining linin fibres. He describes the nucleolus as a compound structure 
made up of a number of deeply staining chromatic masses or granules 
embedded in a more faintly staining matrix. In the prophase, a long spireme 
thread develops in contrast to the short thread described by Lewis for 
Riccio carpus natans. The reduced number of chromosomes is seven 
or eight. 
The spore mother-cells in Riccia Frostii afford only fair material for 
study. Although the cells and the nuclei are large, the spindle is small 
and the chromatin scanty. Almost all stages of division can be found in 
a sporophyte containing active spore mother-cells. The spore mother-cell 
in Fig. 26 presents the characteristic resting-stage of the nucleus, with 
a large nucleolus containing a few vacuoles. The rest of the nuclear content 
is distributed in a fine network around the nucleolus, not entirely filling 
the nuclear cavity. The exact nature of this is difficult to determine, as 
it stains very faintly. The cytoplasm, like that described by Lewis for 
Ricciocarpus natans , consists of a fine reticulum thickly embedded with 
granules. The black globules are especially prominent around the nucleus. 
The spore mother-cells are spherical, lying free in the cavity of the 
sporophyte, surrounded by a semi-fluid substance. In all sporophytes 
found at this stage, the spore mother-cells were not crowded, there often 
being the width of a cell between one and its neighbours. The next stage 
observed (Fig. 27) shows the nucleus somewhat enlarged and elongated. 
Fibres are seen around the nucleus, and in a section showing the surface 
of this nucleus fibres extend across it. The chromatin is in the form of 
irregular lumps. Little is seen in the nucleus besides these lumps of densely 
staining chromatin. The formation of the spindle, from the stage seen in 
Fig. 27, was not observed. Some of the spindles found had decidedly 
pointed poles, but there was no indication of a centrosome or a centrosphere. 
The metaphase is seen in Fig. 28. The chromosomes appear as irregular 
dots, but are very short, curved rods. The cytoplasm in this and succeed- 
ing divisions remains the same. The spindle fibres are very distinct, some 
