MITOSIS IN POLLEN MOTHER-CELLS. 25 
The young weft-like nuclear membrane encloses a cavity containing 
the chromatin and little or no other staining material. With further 
development the kinoplasmic weft is transformed into the typical 
nuclear membrane, appearing in section as a sharp line, and the 
daughter spirem becomes loose and open. In the mature daughter 
nucleus the spirem is continuous and of a tolerably uniform thickness. 
In some cases it is rather regular, consisting of long turns arranged in 
the form of a wreath (Fig. 10, K), but in the majority of instances 
the spirem is irregular, with long and short turns so disposed that its 
course cannot be easily followed. This condition of the spirem is in 
all probability due to the variously shaped chromosomes mentioned 
in a preceding paragraph. 
THE NUCLEOLUS. 
In the resting nucleus and during the prophase, one or more nucle- 
oli are present. These nucleoli take on a deep red or reddish purple 
color with the Flemming triple stain. They sometimes present a uni- 
form structure, but, as a rule, the larger nucleoli especially reveal one 
or more vacuoles. As has been mentioned in a preceding paragraph, 
the nucleolus very frequently lies within a spherical space which 
appears in optical section as a colorless court about it. This phe- 
nomenon is especially striking in vegetative cells of higher plants, 
such as in root tips of Vicza faba and Zea mays. Experiments 
seem to show that the colorless space surrounding the nucleolus 
contains something more than a mere watery fluid which is extracted 
in dehydration. By subjecting roots of Victa, Zea and others to a 
strong centrifugal force, the author (Mottier, ’99) found that the 
nucleolus together with its surrounding colorless court was thrown 
out of the nucleus into the cytoplasm. The expelled nucleolus was 
still surrounded by its colorless court—a fact that seems to show that 
the colorless substance has a specific gravity much greater than other 
constituents of the nucleolus, and that it may be provided with its own 
membrane. This colorless substance may represent unorganized 
nucleolar matter. 
Frequently before the nuclear membrane disappears a disorganiza- 
tion begins by which the nucleolus is broken up into several smaller 
nucleoli (Fig. 6, C). As the nuclear membrane fades away, and the 
kinoplasmic fibers enter the nuclear cavity, numerous bodies are found 
distributed in the cytoplasm which stain exactly as nucleoli, and there 
is no doubt that these bodies represent nucleolar substance. These 
extra-nuclear nucleoli were found to be more abundant in Leléum 
martagon. In Lilium candidum there may be none, or only a few 
