Davis.—Cytological Studies on Oenothera . II. 647 
towards the centre of the nucleus. During the process of contraction 
numerous threads are differentiated from the reticulum and lie in compli¬ 
cated coils. Although it is frequently possible to find threads that run 
closely parallel with one another, the writer is unable to present any 
evidence that this condition is other than such an association as would be 
brought about by the gathering together of a complexly looped thread, or 
system of threads, in a tight mass. 
4. The synaptic contraction draws the coils of threads into a dense 
knot close to the nucleolus, which generally lies at one side of the nucleus. 
A few loops and delicate strands extend into the nuclear cavity from 
the synaptic knot as a centre. The threads gradually thicken as 
synapsis proceeds, and the length of the thread system becomes materially 
shortened. 
5. The chromatic material emerges from synapsis by a loosening of 
the coils of the contracted thread system, when it becomes evident that the 
threads are very much shorter and thicker, although still complexly looped 
and coiled. From this condition is developed by further contraction a very 
much thicker thread which becomes the spireme. 
6 . The spireme by segmentation gives rise to the fourteen sporophytic 
(somatic) chromosomes, which are therefore arranged end to end. These 
chromosome segments continue the process of contraction, which has been 
going on in the spireme, until their long diameter is not more than two or 
three times their width, and the spireme becomes so much shortened that 
the complexities of the looped arrangement largely disappear, and it is 
possible to follow the chain of fourteen chromosome segments for the 
entire length of the spireme. 
7. The condensation and shortening of the spireme frequently draws 
the chromosome segments into a close group, giving the condition described 
as a < second contraction ’. It is, however, doubtful if this stage is a regular 
occurrence or of especial significance. 
8 . The chromosome segments of the spireme break apart during the 
prophase of the heterotypic mitosis, and by further contraction and bending 
in the middle region become the fourteen V-shaped chromosomes charac¬ 
teristic of this mitosis. The chromosomes are all essentially similar to one 
another. 
9. Although not infrequently found in pairs the chromosomes have 
generally a scattered distribution at the equatorial plate, which may give an 
opportunity for numerical irregularities in their distribution by the hetero¬ 
typic mitosis. 
10. The fourteen sporophytic (somatic) chromosomes are distributed as 
two sets by the heterotypic mitosis, which is therefore a reduction division. 
11. A lengthwise fission of each chromosome, in preparation for the 
homotypic division, becomes apparent during the anaphase of the hetero- 
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