Download 136 color, while the cytoplasm is of a brownish hue. The cytoplasm

136
Botanisches Centralblatt. — Beiheft 2.
color, while the cytoplasm is of a brownish hue. The cytoplasm
presents a regular fibrillar or alveolar arrangement. (Figs. 1 and
3.) The meshes especially in the younger cells are very small
and their regularity in many cases is very striking. The cyto­
plasm , however, does not retain its homogeneous structure
throughout the entire course of karyokinesis. B y the time the
splindle is mature that portion of the cytoplasm immediately
surrounding it has become very dense while the remaining
cytoplasm reveals larger meshes and is less granular.
In width
this layer of protoplasm extends one half the distance across the
cell (Figs. 3, 4, 5). Its margin is deeply wavy so that at places
it approaches quite near the cell-wall. The remaining protoplasm
of the cell has also changed for its meshes (Fig. 4) appear to be
five or six times as large as they were in the earlier stages. The
regularity of the protoplasmic meshes are now clearly less regular
in outline. An examination of hundreds of specimens confirmed
the above statements in every case.
Development
of the
chromosomes.
In the very early stages the nucleus, as above stated, pre­
sents a fine linin net. The threads of the net are at first smooth
and uniform in diameter. In nuclei, however, which have ad­
vanced slightly beyond the resting stage the linin-net begins to
show irregularities in width due to the appearance of larger
granules. These granular masses constitute the chromatin. They
are irregularly distributed in the linin net-work, and increasing
in size ultimately form the chromosomes. A continuous chromatin
It will be
spirem does not seem to be developed in Magnolia.
seen further that the nucleolus at this stage (Fig. 1) is very large
staining densely and contains a conspicuous vacuole. The fibres
of the linin network run to the nucleolus and are attached to it
in such a way that a slight enlargement at the point of contact is
visible. This was always found to be the case whether one or
several nucleoli were present.
These filiaments radiating from
many points on its periphery seem to hold it in position. Its
position was influenced in the direction of attachment of the
greatest number of nuclear fibres (Fig. 1).
At a later stage of karyokinesis (Fig. 2) we find that the
nucleolus has entirely disapeared. It is probably utilized as food
in the growth of the chromatin masses, for they stain much more
readily and intensely at this time than at an earlier stage. The
nuclear membrane which is now less distinct is gradually replaced
by a weft of filaments closely interwoven. The threads of this
weft are very fine, and the most careful staining is necessary to
bring them out.
The different forms which the chromosomes assume at this
stage (Fig. 2) are due to a total or partial longitudinal splitting
and a subsequent bending. This longitudinal cleavage is recognized
as a rather clear line which appears through the length of the
chromosome (Fig. 2). After this division the chromosomes bend