130
LUISE STANGE
the functions of division do not 'age' but remain unaltered in contrast to
the progressing changes in the cells in the light. It should be mentioned,
that the darkness cannot have a generally retarding influence on ageing,
since the cells at the base of the plant die earlier in the dark than in the
light. It can be concluded from these results that ageing in these cells, in
the sense of a withdrawal from divisional functions, is caused by some
influence of light or by some functions possible only in the light.
The preceding investigations were all carried out with isolated whole
parts of the plants (e.g. leaves or thallus fragments). However, completely different results were obtained after isolation of single cells of
different age in fern prothallia. In the isolated single cell there is the
advantage that the behaviour of the cell is completely free of influences
of neighbouring cells. Already Linsbauer (1926) and Meyer (1953) had
observed occasionally regeneration of complete new plants from single
isolated cells of fern prothallia (cf. also Zepf, 1952, for Sphagnum). Ito
(1960, 1962) succeeded in regenerating to a great extent whole plants
from single cells of gametophytes of Pteris vittata after operative
isolation. Isolation of a cell was carried out by pricking and killing the
surrounding cells with a fine glass needle. The cells were isolated from
the protonema portion and the unistratose part of the prothallium,
where they have a length of over 30 μ. Isolation of the cells in the
meristematic region in which the cells are very small was not possible.
Every single isolated cell regenerated and grew out to a mature gametophyte. Only rhizoidal cells showed no regeneration when isolated. The
onset of regeneration is characterized by the formation of a rhizoid.
After rhizoid formation the isolated cell begins to swell in a certain part
and then divides into two unequal cells. The smaller cell continues to
divide giving rise to a filamentous protonema. To compare the regenerative ability of cells of different age, the time interval between isolation
and the formation of the first protonema cell as criterion for the onset
of regeneration was determined. The marginal cells of the wing and the
cells of the filamentous part were numbered from the base to the apex.
Each second cell was isolated by killing the neighbouring cells. The
results are represented in Fig. 5a. While the cells nearest to the base
needed 3-4 days for the production of the first protonema cell, the cells
near the apical meristem formed the first protonema cell only after 18
days. A clear relationship exists between the regenerative ability of
each single cell and its age; cells near the base, which are older, regenerate more easily and the farther from the base the cells are located
the more time elapses till they begin to regenerate. The time interval
between isolation and rhizoid formation shows the same dependence on
the age of the isolated cells. These results are unexpected, since in the
whole organism the cells in the apical region are still actively dividing,
LUISE STANGE
the functions of division do not 'age' but remain unaltered in contrast to
the progressing changes in the cells in the light. It should be mentioned,
that the darkness cannot have a generally retarding influence on ageing,
since the cells at the base of the plant die earlier in the dark than in the
light. It can be concluded from these results that ageing in these cells, in
the sense of a withdrawal from divisional functions, is caused by some
influence of light or by some functions possible only in the light.
The preceding investigations were all carried out with isolated whole
parts of the plants (e.g. leaves or thallus fragments). However, completely different results were obtained after isolation of single cells of
different age in fern prothallia. In the isolated single cell there is the
advantage that the behaviour of the cell is completely free of influences
of neighbouring cells. Already Linsbauer (1926) and Meyer (1953) had
observed occasionally regeneration of complete new plants from single
isolated cells of fern prothallia (cf. also Zepf, 1952, for Sphagnum). Ito
(1960, 1962) succeeded in regenerating to a great extent whole plants
from single cells of gametophytes of Pteris vittata after operative
isolation. Isolation of a cell was carried out by pricking and killing the
surrounding cells with a fine glass needle. The cells were isolated from
the protonema portion and the unistratose part of the prothallium,
where they have a length of over 30 μ. Isolation of the cells in the
meristematic region in which the cells are very small was not possible.
Every single isolated cell regenerated and grew out to a mature gametophyte. Only rhizoidal cells showed no regeneration when isolated. The
onset of regeneration is characterized by the formation of a rhizoid.
After rhizoid formation the isolated cell begins to swell in a certain part
and then divides into two unequal cells. The smaller cell continues to
divide giving rise to a filamentous protonema. To compare the regenerative ability of cells of different age, the time interval between isolation
and the formation of the first protonema cell as criterion for the onset
of regeneration was determined. The marginal cells of the wing and the
cells of the filamentous part were numbered from the base to the apex.
Each second cell was isolated by killing the neighbouring cells. The
results are represented in Fig. 5a. While the cells nearest to the base
needed 3-4 days for the production of the first protonema cell, the cells
near the apical meristem formed the first protonema cell only after 18
days. A clear relationship exists between the regenerative ability of
each single cell and its age; cells near the base, which are older, regenerate more easily and the farther from the base the cells are located
the more time elapses till they begin to regenerate. The time interval
between isolation and rhizoid formation shows the same dependence on
the age of the isolated cells. These results are unexpected, since in the
whole organism the cells in the apical region are still actively dividing,