Gates. — Somatic Mitoses in Oenothera. 1007 
somes which separated precociously may merely segregate in metaphase 
instead of dividing again, and thus restore the normal number. 
From the various counts now made it is evident that more individuals 
of the mutant O. lata contain 15 chromosomes than 14, and it may be that 
the O. lata characters are constantly associated with the presence of an 
extra chromosome. 
The account of somatic mitosis is taken entirely from the nucellus, 
though the phenomena are closely similar in other tissues. The resting 
nucleus contains a uniform reticulum of somewhat moniliform threads. 
There is no evidence whatever of prochromosomes or denser chromatic 
centres in the completely resting nucleus. 
The chromosomes first appear in early prophase by a thickening 
in certain threads of the reticulum. They are at first long and narrow, 
much twisted, and are not evidently paired in any way, but are scattered 
irregularly through the nucleus, being connected by a meshwork of finer 
threads. 
The chromosomes then shorten and thicken, the finer threads gradually 
disappear, and the chromosome bodies can easily be counted. 
A conspicuous longitudinal split then, usually at least, appears in the 
chromosomes in the late prophase shortly before the nuclear membrane 
disappears. The first evidence of lateral pairing of the chromosomes also 
appears about this time. 
In the latest prophase stage, after the nuclear membrane has dis- 
appeared and the spindle has begun to form, the split in the chromosomes 
may close up entirely. 
In metaphase the chromosomes are often in evident pairs on the 
equatorial plate, it being possible in some cases to determine with a high 
degree of probability the particular chromosome which is odd and unpaired. 
Certain cases are described in which the chromosomes in metaphase 
differed from the normal in shape, being shorter and thicker and more like 
the heterotype chromosomes, or dumb-bell shaped like the somatic chromo- 
somes in one stage of the telophase. 
In the very early telophase, after the nuclear membrane is formed, the 
chromosomes, at least in many cases, assume a characteristic dumb-bell 
shape owing to a median constriction. The chromosomes continue to be 
countable until a later stage, but finally pass into a completely resting con- 
dition in which no remnant of a central denser core of the chromosome 
remains. 
It was discovered accidentally that if the wall of a cell in a preparation 
be ruptured and the contents squeezed out, the spindle may be isolated and 
retain its shape and the chromosomes remain attached, showing that it has 
greater stability of structure than would be produced by osmotic or electro- 
magnetic forces. 
