REGENERATION IN LOWER PLANTS
121
a narrow marginal zone of the wing fragment. It was clear in this
material that movements of cellular components were always preceded
by the increase in nucleolar size. The nucleus then moves from its
position close to a cell wall perpendicular to the plane of the wing to a
more central position in the cell and the chloroplasts migrate along
cytoplasmic strands toward the nucleus and form a cluster around it
(Fig. 2).
These movements of the nucleus and the chloroplasts have been
studied in detail in cells of detached leaves of the moss Splachnum
ampullaceum (von Maltzahn and MacNutt, 1960). One early sign that a
cell is in a process of fundamental changes is the formation of intravacuolar cytoplasmic strands. In a mature cell of the leaves of Splachnum the cytoplasm is restricted to a thin layer along the cell walls
surrounding a large vacuole. The nucleus is in a peripheral position.
Within a few hours after isolation intravascular strands are formed, a
primary one connecting the cytoplasm around the nucleus with the
cytoplasm at the opposite cell wall across the vacuole. Strand formation reaches a maximum between 24 and 48 h after isolation. Intravacuolar strand formation is followed by the movement of the nucleus
and the chloroplasts via the cytoplasmic strand to a more central position in the cell. The result is the formation of a cluster of cytoplasm and
chloroplasts around the nucleus (systrophe). Cytoplasmic migration is
the primary event in these movements. In further investigations (von
Maltzahn, 1961) it became evident that the cytoplasmic strands
originate by the formation of secondary vacuoles. These vacuoles are
formed in various parts of the peripheral cytoplasm, predominantly in
the vicinity of the nucleus. The position of the clusters of cytoplasm and
chloroplasts inside the cells was examined in the surface plane. In most
cells the clusters showed random distribution without any preference
for positions toward the tip, the base, the margin or the midrib of the
leaf or the centre of the cell. Only in cells near a wound surface, the
clusters exhibited an orientation toward the wound surface regardless
of its relation to the longitudinal axis of the leaf. Random distribution
of the clusters in the cells is taken by MacNutt and von Maltzahn (1960)
as evidence for the assumption that the process of cellular ^differentiation' results in the loss of cellular polarity.
Also in the cells of detached leaves of Splachnum a considerable
increase in nucleolar size was observed. By measuring the diameter of
nuclei it could be shown that 24 h after isolation of the leaves a significant increase in nuclear size is reached. Division of the nucleus occurs
between 48 and 60 h after isolation. Increase in nuclear and nucleolar
size is taken as indication of renewed synthetic activities in the cell.
In further investigations with Splachnum, MacNutt and von Malt-
121
a narrow marginal zone of the wing fragment. It was clear in this
material that movements of cellular components were always preceded
by the increase in nucleolar size. The nucleus then moves from its
position close to a cell wall perpendicular to the plane of the wing to a
more central position in the cell and the chloroplasts migrate along
cytoplasmic strands toward the nucleus and form a cluster around it
(Fig. 2).
These movements of the nucleus and the chloroplasts have been
studied in detail in cells of detached leaves of the moss Splachnum
ampullaceum (von Maltzahn and MacNutt, 1960). One early sign that a
cell is in a process of fundamental changes is the formation of intravacuolar cytoplasmic strands. In a mature cell of the leaves of Splachnum the cytoplasm is restricted to a thin layer along the cell walls
surrounding a large vacuole. The nucleus is in a peripheral position.
Within a few hours after isolation intravascular strands are formed, a
primary one connecting the cytoplasm around the nucleus with the
cytoplasm at the opposite cell wall across the vacuole. Strand formation reaches a maximum between 24 and 48 h after isolation. Intravacuolar strand formation is followed by the movement of the nucleus
and the chloroplasts via the cytoplasmic strand to a more central position in the cell. The result is the formation of a cluster of cytoplasm and
chloroplasts around the nucleus (systrophe). Cytoplasmic migration is
the primary event in these movements. In further investigations (von
Maltzahn, 1961) it became evident that the cytoplasmic strands
originate by the formation of secondary vacuoles. These vacuoles are
formed in various parts of the peripheral cytoplasm, predominantly in
the vicinity of the nucleus. The position of the clusters of cytoplasm and
chloroplasts inside the cells was examined in the surface plane. In most
cells the clusters showed random distribution without any preference
for positions toward the tip, the base, the margin or the midrib of the
leaf or the centre of the cell. Only in cells near a wound surface, the
clusters exhibited an orientation toward the wound surface regardless
of its relation to the longitudinal axis of the leaf. Random distribution
of the clusters in the cells is taken by MacNutt and von Maltzahn (1960)
as evidence for the assumption that the process of cellular ^differentiation' results in the loss of cellular polarity.
Also in the cells of detached leaves of Splachnum a considerable
increase in nucleolar size was observed. By measuring the diameter of
nuclei it could be shown that 24 h after isolation of the leaves a significant increase in nuclear size is reached. Division of the nucleus occurs
between 48 and 60 h after isolation. Increase in nuclear and nucleolar
size is taken as indication of renewed synthetic activities in the cell.
In further investigations with Splachnum, MacNutt and von Malt-