1908] GATES—REDUCTION IN OENOTHERA 3 
notable advantage in comparing this with other studies in reduction 
is in the shape of the chromosomes, which are globular or somewhat 
oblong or cylindrical in most stages of mitosis, and are never greatly 
elongated or looped. For this reason it is a comparatively easy 
matter to obtain accurate counts of the chromosomes in the pollen 
mother cells of any of the forms. This shape is also found to be very 
advantageous in a study of the events of reduction following synapsis. 
The appearances are clear and easily interpreted, in striking contrast 
to the forms with long twisted chromosomes, such as have been made 
the basis of many of the studies on reduction in plants. 
On the other hand, the somatic nuclei and chromosomes are very 
much smaller, and in metaphase the latter are elongated and looped, 
making it impossible to count them with the same degree of accufacy. 
Some of these appearances have already been described elsewhere 
(12, p. 19). Thus while it was found that the chromosomes could 
be counted almost equally well in pollen mother cells of all the 
forms studied, O. rubrinervis was found to be especially favorable 
for the investigation of reduction phenomena, especially the events 
of synapsis and the prophases of the heterotypic mitosis. The 
account given here will refer throughout to O. rubrinervis, with 
occasional comparisons with other forms. Later papers will take 
up these other forms in detail, in so far as this is necessary after the 
account presented here. Special attention will be given at that time, 
in particular, to the later stages, beginning with the telophase of 
the heterotypic mitosis, and also to the interesting conditions in some 
of the hybrids. The detailed account in O. rubrinervis will not be 
carried farther than the metaphase of the heterotypic mitosis, at 
which time the essential events have already taken place. 
Methods 
The usual methods of cytological technique were employed, 
Various chrom-acetic and chrom-osmo-acetic solutions being tried 
until satisfactory fixation was obtained. The thickness of the sec- 
Hons varied from 4 to rom#. The latter thickness was found most 
favorable for counting chromosomes, because it is somewhat greater 
than the diameter of the nuclei, many of which in such sections were 
therefore uncut. It is possible to determine easily whether a nucleus 
has been cut by the knife by examining it in low and high focus. ‘The 
