637 
Davis .— Cylological Studies on Oenothera. II. 
other strains of the variable 0 . grandiflora showed departures from the 
conditions in the material described by the writer, and that following 
synapsis types of chromosome organization will be found which resemble 
more closely those of O. biennis. 
The important point to emphasize in this connexion is that in both 
grandiflora and biennis the chromosomes are organized from segments 
of a spireme arranged end to end, and that the history of the reduction 
divisions in this respect is the same as that described by Gates (’ 08 ) for 
rubrinervis and Geerts ( 09 ) for Lamarckiana. 
The Heterotypic Mitosis. The condensation of the chromatin, which 
takes place during the organization of the spireme and formation of the 
chromosomes, continues throughout the prophases of the first, or heterotypic, 
division. As a result the chromosomes at metaphase of this mitosis 
(Figs. 22 and 23) are very much smaller structures than the segments of the 
spireme (Figs. 13 and 14) from which they are derived. The mature chromo¬ 
somes are essentially similar, generally with the form of thickened V’s due 
to the bending of the spireme segments, and are not rounded structures such 
as have been described and figured by Gates and Geerts. 
The process of spindle formation is the same as that of grandiflora , 
and similar to that described for a number of higher plants (e. g. Eqnisetum , 
Larix , Lilium, &c.). Fibrillae enter the nuclear cavity with the breaking 
down of the nuclear membrane, and also push out into the cytoplasm 
in various directions and thus establish a multipolar spindle (Figs. 19 and 
20) ; the large nucleolus disappears at an early stage in the process. The 
group of chromosomes is brought by the development of the fibres to the 
centre of the spindle where the chromosomes lie in irregular clusters, in 
which, however, some may frequently be found still united end to end 
in short chains of two to five chromosomes. 
The multipolar condition of prophase gradually changes to a typical 
bipolar spindle characteristic of metaphase (Figs. 21-23) by a rearrangement 
and gathering of the spindle fibres into two broad sheaves which end in 
granular areas that merge with the alveolar cytoplasm. During this 
development the chromosomes separate from one another and usually 
take on the form of thickened V’s by the bending of the ends and the 
thickening of the chromatin in the middle regions. The arrangement of 
the chromosomes as they are brought to the equatorial plate during 
metaphase is quite irregular. Although occasional pairs are found 
sufficiently closely associated to indicate that they were adjacent segments 
of the spireme, most of the chromosomes are so separated and scattered 
(Figs. 21 and 22) that it is impossible to determine with certainty what was 
their relation to one another in the spireme. 
In this respect these conditions in biennis are in sharp contrast to those 
in the material of grandiflora, studied by the writer, where the arrangement 
