REGENERATION IN LOWER PLANTS
141
expense of substances synthesized or mobilized in the mature cells. If
fragments, cut from plants which have been in the dark for 10 days,
are kept further in the dark, no signs of regeneration can be observed.
But regeneration starts without any delay as soon as the fragments are
exposed to light (Stange, 1957). However, it is obvious that no regeneration, i.e. growth processes, can take place without supply of precursors and energy which in green plants derive finally from photosynthesis (cf. Stange, 1960; also Hämmerling, 1958). Thus, no decision
between the two hypotheses is possible from these experiments.
The influence of indoleacetic acid (IAA) on regeneration by way of
embryonization has been examined by various investigators. In his
experiments with prothallia of the fern Pteris longifolia, Albaum (1938b)
removed the apical meristem and placed the cut surfaces of the basal
parts in contact with solutions of IAA (10
- 4
and 10
- 5
g/ml) or applied
IAA-lanoline paste (10
- 2
g/g) to the apical cut surfaces of the basal
parts. IAA in these concentrations inhibited the outgrowth of adventitious prothallia almost completely. This result is taken as evidence for
the idea that, in the intact plant, growth hormone coming from the
apex of the prothallium inhibits the outgrowth of adventitious prothallia from the mature cells. No cytological examination of the cells of
the basal part has been reported. In later investigations with other
material (see below) it has been repeatedly shown that the concentrations of IAA used in this experiment caused damage to the treated cells.
In experiments with Funaria hygrometrica, Bopp (1953) could not
detect an inhibition of regeneration by IAA. Isolated leaves on agar
containing 10
- 8
to 10
- 5
g/ml IAA, regenerated protonema, while in the
concentrations of 5 x 10
- 5
and 10~
4
g/ml no regeneration occurred. In
these high concentrations the chloroplasts degenerated and the leaves
were damaged irreversibly. A clear influence of IAA on bud formation
at the protonema was reported. While in the concentration 10
- 8
g/ml the
number of buds was increased compared to the control without IAA, in
the concentration 10
- 6
and 10
- 5
g/ml the number of buds decreased. I t
was often observed that, under the influence of IAA, the three-sided
apical cell of a newly formed bud grew out to a protonema filament after
only a few divisions, or that after the formation of a small bud all cells
changed again into protonema growth. Experiments with isolated tissue
of Biella led to comparable results (Stange, 1955, 1957, 1958). While
concentrations of IAA of 10
- 4
and 7-5 x 10~
5
g/ml proved toxic, regeneration occurred in the concentration range 5 x 10~
5
to 10
- 9
g/ml. With
increasing concentration the regenerates were formed with more and
more delay and had, in the higher concentrations, a strongly modified
appearance. In the concentrations 10~
7
and 10~
6
g/ml they were composed predominately of large cells and formed repeatedly local growth
141
expense of substances synthesized or mobilized in the mature cells. If
fragments, cut from plants which have been in the dark for 10 days,
are kept further in the dark, no signs of regeneration can be observed.
But regeneration starts without any delay as soon as the fragments are
exposed to light (Stange, 1957). However, it is obvious that no regeneration, i.e. growth processes, can take place without supply of precursors and energy which in green plants derive finally from photosynthesis (cf. Stange, 1960; also Hämmerling, 1958). Thus, no decision
between the two hypotheses is possible from these experiments.
The influence of indoleacetic acid (IAA) on regeneration by way of
embryonization has been examined by various investigators. In his
experiments with prothallia of the fern Pteris longifolia, Albaum (1938b)
removed the apical meristem and placed the cut surfaces of the basal
parts in contact with solutions of IAA (10
- 4
and 10
- 5
g/ml) or applied
IAA-lanoline paste (10
- 2
g/g) to the apical cut surfaces of the basal
parts. IAA in these concentrations inhibited the outgrowth of adventitious prothallia almost completely. This result is taken as evidence for
the idea that, in the intact plant, growth hormone coming from the
apex of the prothallium inhibits the outgrowth of adventitious prothallia from the mature cells. No cytological examination of the cells of
the basal part has been reported. In later investigations with other
material (see below) it has been repeatedly shown that the concentrations of IAA used in this experiment caused damage to the treated cells.
In experiments with Funaria hygrometrica, Bopp (1953) could not
detect an inhibition of regeneration by IAA. Isolated leaves on agar
containing 10
- 8
to 10
- 5
g/ml IAA, regenerated protonema, while in the
concentrations of 5 x 10
- 5
and 10~
4
g/ml no regeneration occurred. In
these high concentrations the chloroplasts degenerated and the leaves
were damaged irreversibly. A clear influence of IAA on bud formation
at the protonema was reported. While in the concentration 10
- 8
g/ml the
number of buds was increased compared to the control without IAA, in
the concentration 10
- 6
and 10
- 5
g/ml the number of buds decreased. I t
was often observed that, under the influence of IAA, the three-sided
apical cell of a newly formed bud grew out to a protonema filament after
only a few divisions, or that after the formation of a small bud all cells
changed again into protonema growth. Experiments with isolated tissue
of Biella led to comparable results (Stange, 1955, 1957, 1958). While
concentrations of IAA of 10
- 4
and 7-5 x 10~
5
g/ml proved toxic, regeneration occurred in the concentration range 5 x 10~
5
to 10
- 9
g/ml. With
increasing concentration the regenerates were formed with more and
more delay and had, in the higher concentrations, a strongly modified
appearance. In the concentrations 10~
7
and 10~
6
g/ml they were composed predominately of large cells and formed repeatedly local growth