UNIVERSITATIS LATVIENSIS - DSpace

the tapetum cells are usually not so large as in the other part,
which is turned to the centre of the anther. It is possible
that this inner part of the tapetum
material,
the other part.
cells receives more untritive
because it is situated nearer the vascular bundle than
The tetrad division (Fig. 4) compared with the typical
tetrad division, shows no peculiarities. The division, generally
in the stage of equatorial plate, offers a good opportunity for
counting the chromosomes. There are 7 chromosomes (Fig. 1).
It is also possible to count the chromosomes in the diploid
cells, near the flower (Fig. 18).
The number of the bivalent
chromosomes on the equatorial plate can with certainty be counted
as 14. The diploid chromosomes are larger than the haploid
ones, differing especially in length.
Some of the chromosomes
of the daughter nuclei are left behind, when all are making their
way to the poles of the spindle. Such slowly travelling chro-
mosomes are also noticed in some cases of mitotic division in
the tapetum cells.
During the interkinesis the chromosomes in the nuclei of
dyads are dispersed into grains. The nuclei instead of the
spindle remain united to each other by a bridge of thick plasma
(Fig. 2). In the second phase of the division both figures of
the spindles lie perpendicularly
126
under each other or at a more
or less acute angle, but a parallel position of the spindles is
also sometimes noticed. The chromosomes after division form
the four nuclei of the tetrad, the strings of plasma between
them can be observed for some time. These plasma formations
are observed not only between the daughter nuclei,
but also
between all four nuclei. Afterwards these formations disappear
and the nuclei form the characteristic position of a
every position of the tetrade all four nuclei can
tetrad. In
be seen in the
preparations stained wity gentiana-violett-eosin, the blue nuclei
in that case shine through the red plasma. The pollen during
the formation of nuclei enlarges the quantity of plasma.
The division
of the nucleus into a vegetative one and a generative one has some-
times been observed. Pollen with three nuclei has not been noticed.
The development of the embryo-sac begins with the inten-
sive division of epidermal and subepidermal cells in those places
where the embryo-sacs are to be formed,
and there therefore can
be observed little protuberances (Fig. 8). The cells of the
young embryo-sac in the early stages are very rich in plasma
and in the stained preparations are more deeply
the other cells in the neigbourhood (Fig. 9).
stained then
At the distance
of about
30|i from the top of the protuberance appear
the inte-
guments, first the inner and a little lower the outer,
both in the