950 Davis.—A Comparison of the Reduction Divisions of 
biennis . These cases in both biennis and Lamarckiana are of great interest, 
but it should be noted that they are rare, and it would be quite impossible 
to find sufficient material to determine whether or not fertile pollen-grains 
can be developed with nuclei bearing a greater or less number of chromo¬ 
somes than the normal. 
The group of seven split chromosomes is best observed in polar views 
of late anaphase, and at the time of the reconstruction of the daughter 
nuclei. Their history may be readily followed through the interkinesis 
between the heterotypic and homotypic mitoses. Following the organiza¬ 
tion of the daughter nuclei, the halves of each chromosome bend so that 
they separate at the ends, and thus come to have the form of two U’s joined 
together in the middle region (PI. LXXI, Fig. 31; PI. LXXII, Figs. 32, 33). 
The seven split chromosomes become therefore seven evident pairs, the 
members of each pair remaining in close association until the metaphase 
of the homotypic mitosis. The chromosomes during the reconstruction 
of the daughter nuclei increase rapidly in size, and remain in this expanded 
state throughout the interkinesis. Nucleoli appear (Fig. 33) and sometimes 
the ends of the chromosomes proliferate and show a tendency to form an 
imperfect network. The period of interkinesis is of considerable length, 
with the individuality of the chromosomes generally maintained quite as 
clearly as is indicated in Figs. 31-33, and this history is the same in all 
essentials as that in biennis and grandiflora and agrees with the accounts 
of Gates and Geerts. 
In summary of the events of the heterotypic mitosis in Lamarckiana 
it should be noted (r) that the fourteen V-shaped sporophytic (somatic) 
chromosomes are distributed in two groups of seven each, so that the 
mitosis is a reduction division ; (2) that the chromosomes are assembled 
irregularly at the equatorial plate, and that there is no uniform grouping of 
the structures in pairs, although occasional pairs may be found ; (3) that the 
chromosomes are essentially similar to one another in form and size; and 
(4) that during anaphase there is a fission of the chromosomes, so that seven 
split chromosomes enter each daughter nucleus and are evident as seven 
pairs during the period of interkinesis. 
The Homotypic Mitosis. The appearance of a web of fibrillae around 
the resting nucleus of the interkinesis together with the breaking down of 
its membrane indicates the approach of the homotypic mitosis. The fibrillae 
enter the nuclear cavity and establish a multipolar spindle (PI. LXXII, 
Figs. 34 and 35), at the same time carrying the seven pairs of chromosomes 
towards the centre of the structure. A bipolar spindle is then developed 
by the rearrangement of the fibres, and the pairs of chromosomes become 
grouped upon an equatorial plate (Fig. 36) so that the members of the 
pairs will be separated and distributed by the mitosis with perfect regu¬ 
larity, seven chromosomes in each set. The two homotypic spindles in the 
