Davis. — Cytological Studies on Oenothera. I. 565 
cavity and which segments crosswise to form a chain of fourteen chromo- 
somes. 
2. Pairs of chromosomes may be precociously cut off from the 
spirem, the members of the pairs bending around to form loops but never 
becoming united to form rings. 
3. The chromosome segments are at first several times longer than 
broad, but by a process of condensation become nearly globular or pear- 
shaped. 
4. The chromosomes are at first arranged irregularly on the hetero- 
typic spindle, many of them frequently remaining separate and unpaired. 
5. Such a distribution allows irregularities of distribution in the 
heterotypic mitosis, so that both (unpaired) chromosomes belonging to one 
pair will occasionally enter the same daughter-nucleus. 
It seems to the writer best to defer a detailed discussion of the cyto- 
logical problems touched by the present study until further investiga- 
tions have been made on this interesting genus, but a few important con- 
siderations may be briefly outlined. 
It is clear for Oenothera grandiflor a that the sporophytic chromosomes 
become associated in ring-shaped pairs, which first appear as the chromatin 
emerges from synapsis, and are characteristic of the period termed dia- 
kinesis and of the prophases leading to the heterotypic mitosis. These ring- 
shaped bivalent chromosomes are assembled in a very orderly manner at 
the equatorial plate of the heterotypic mitosis, where they remain intact 
as rings until the separation of their halves into two numerically equivalent 
sets of sporophytic chromosomes. There is little or no opportunity for 
irregularities in the distribution of the numbers when the normal processes 
of the mitosis follow such a history. 
The V-shaped sporophytic chromosomes of the heterotypic mitosis 
are in general similar to one another in form and size. There is apparently 
no more variation in these respects than is shown in the heterotypic mitosis 
of plants in general. The condition as illustrated in Fig. 37 is the normal 
one for this form, and variations from this as shown in Fig. 38 indicate 
only that certain rings (bivalent chromosomes) occasionally lag behind the 
others in completing the separation of the sporophytic chromosomes. 
The chromosomes may readily be followed between the telophases 
of the heterotypic and the prophases of the homotypic mitoses, maintaining 
their individuality with very little change of form throughout this period 
of interkinesis. This history has also been noted by Gates and Geerts in 
O. Lamarckiana and O. rnbrinervis. It adds further evidence against the 
views of Mottier (’03 and ’ 07 ), Lewis (’ 08 ), and others that chromosomes 
lose their individuality in the resting nucleus between the heterotypic and 
homotypic mitoses. 
The interpretation of synaptic and presynaptic conditions presents far 
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