520 Black . — The Morphology of Riccia Rrostii, A test. 
reaching from pole to pole, others ending at the equator, or diverging there 
into the cytoplasm. Fig. 29 shows the chromatin in irregular lumps at the 
poles. The spindle fibres are definite only to the equator, which appears 
granular. In Fig. 30 the daughter nuclei are formed with a definite nuclear 
membrane. They occupy a position very near the wall of the spore mother- 
cell. Spindle fibres still connect the nuclei, some extend into the cytoplasm. 
There is a suggestion of cell-plate formation. The chromatin is in one or 
more irregular clumps, which are embedded in a faintly staining reticulum. 
The next figure (PI. XXXVIII, Fig. 31) shows the nuclei in practically the 
same condition as in Fig. 30, and still very near the periphery of the spore 
mother-cell. An indefinite cell-plate is observed. A few spindle fibres 
extend from the daughter nuclei to the cell-plate. The cell-plate does 
not take in the complete diameter of the cell. In Fig. 32 the daughter 
nuclei have moved from the wall of the mother-cell, and now occupy an 
almost median position in either half of the cell. The cell-plate is distinctly 
granular, and extends only partly across the cell. 
The second division in the spore mother-cell was found to be 
simultaneous in the two daughter nuclei. The spindles may lie in the 
same plane or at right angles to each other (Figs. 33 and 34). The spindle 
fibres are plainly seen, especially those apparently attached to the chromo- 
somes. The spindle tapers to a point at the poles. The chromosome 
appears as a small, irregular-shaped lump, with a suggestion of a curve. In 
the polar views in Figs. 33 and 34, eight chromosomes are counted. No 
definite cell membrane was seen dividing the cell, although there is a sug- 
gestion of cleavage in the contents of the mother-cell between the dividing 
nuclei, indicating that a persistent cell-wall may or may not be formed in 
the first mitosis. Fig. 35 shows the formation of two of the daughter 
nuclei from the second division. The spindle fibres are distinct, but there 
is no indication of a cell-plate, although the cell contents appear divided. 
The daughter nuclei are small, with a very definite nuclear membrane. The 
chromatin is scanty, in several irregular lumps. There has been a gradual 
decrease in the size of the nucleus from spore mother-cell to spore. No 
centrospheres or centrosomes were seen in any stage in the division of the 
spore mother-cell. 
Development of the Spore. 
The development of the protective coverings of spores and pollen- 
grains has received attention by numerous investigators since the publication 
of Strasburger’s work ( 39 ) in 1882. A paper by Fitting (21) gave an impetus 
to further research, by his conclusion that the spore coats in Isoetes and 
Selaginella were formed independently of any direct connexion with the 
protoplasm of the spore. Miss Lyon ( 34 ), in studying the spore coats of 
