R E G E N E R A T I O N IN LOWER PLANTS
145
its regenerating cells can be demonstrated. For instance, when in algae,
bryophytes or fern prothallia, parts are isolated which contain the
apical meristem or apical cell, these parts regenerate only rhizoids (e.g.
Linsbauer, 1926; Czaja, 1930; Müller-Stoll, 1952; Sironval, 1952; Fig.
6). I t must be assumed, as already mentioned (Section I I I , A, 2), that
the rhizoids, besides their function in attachment and water uptake,
have a special metabolic task and constitute one pole of the heteropolar
axis of the plant, like the roots in higher plants. After removal of
rhizoids, apparently a metabolic balance in the apical plant part is disturbed and must be reconstituted. Similarly, a newly formed division
centre in a regenerating fragment of Riella induces other cells engaged
in embryonization to enter the direction of rhizoid development (cf.
Section I I I , B).
In Funaria, it could be shown that the influence of the isolated part
on the differentiation of the regenerate can be based on nutritional
effects (Bopp, 1952). I t was first observed that the differentiation of the
regenerate is dependent on the nature of the isolated part. If protonema
cells were isolated, they regenerated new protonema filaments, which
formed a circular protonema mat. I n the periphery of this mat, a
definite distance from its centre, buds arose after 18-21 days. Isolated
mature leaves of the gametophore produced protonema filaments about
48 h after isolation. After a further 48 h the first buds were formed at
the base of some of these still short filaments. While these buds grew out
to 'primary plantlets' the protonema was further expanding and after
about 10 days further buds ('secondary plantlets') were formed. A different result was obtained when very young leaves were used for the
regeneration experiment. These small leaves in which the rib has not
yet differentiated, very rarely formed 'primary plantlets' from the first
cells of the protonema arising from the leaf, but the protonema grew out
radially to form a protonema mat on which 'secondary plantlets'
appeared. I t could be shown that the size, rather than developmental
stage, of the leaves of different age was responsible for these different
products. After subdividing mature leaves into small enough parts,
these also regenerated a protonema mat of a definite size before buds
were formed. When isolated mature leaves were kept in the dark, only
few protonema filaments grew out from them and no buds were produced. Leaves were exposed to light over various time intervals immediately after isolation and then kept in the dark. The results of these
experiments demonstrated that protonema regeneration is much less
dependent on light than bud formation and that the longer leaves have
been exposed to light the more buds are formed. Experiments in which
photosynthesis was selectively inhibited by sodium fluoride suggest that
this light effect is at least partly due to the production of substances
145
its regenerating cells can be demonstrated. For instance, when in algae,
bryophytes or fern prothallia, parts are isolated which contain the
apical meristem or apical cell, these parts regenerate only rhizoids (e.g.
Linsbauer, 1926; Czaja, 1930; Müller-Stoll, 1952; Sironval, 1952; Fig.
6). I t must be assumed, as already mentioned (Section I I I , A, 2), that
the rhizoids, besides their function in attachment and water uptake,
have a special metabolic task and constitute one pole of the heteropolar
axis of the plant, like the roots in higher plants. After removal of
rhizoids, apparently a metabolic balance in the apical plant part is disturbed and must be reconstituted. Similarly, a newly formed division
centre in a regenerating fragment of Riella induces other cells engaged
in embryonization to enter the direction of rhizoid development (cf.
Section I I I , B).
In Funaria, it could be shown that the influence of the isolated part
on the differentiation of the regenerate can be based on nutritional
effects (Bopp, 1952). I t was first observed that the differentiation of the
regenerate is dependent on the nature of the isolated part. If protonema
cells were isolated, they regenerated new protonema filaments, which
formed a circular protonema mat. I n the periphery of this mat, a
definite distance from its centre, buds arose after 18-21 days. Isolated
mature leaves of the gametophore produced protonema filaments about
48 h after isolation. After a further 48 h the first buds were formed at
the base of some of these still short filaments. While these buds grew out
to 'primary plantlets' the protonema was further expanding and after
about 10 days further buds ('secondary plantlets') were formed. A different result was obtained when very young leaves were used for the
regeneration experiment. These small leaves in which the rib has not
yet differentiated, very rarely formed 'primary plantlets' from the first
cells of the protonema arising from the leaf, but the protonema grew out
radially to form a protonema mat on which 'secondary plantlets'
appeared. I t could be shown that the size, rather than developmental
stage, of the leaves of different age was responsible for these different
products. After subdividing mature leaves into small enough parts,
these also regenerated a protonema mat of a definite size before buds
were formed. When isolated mature leaves were kept in the dark, only
few protonema filaments grew out from them and no buds were produced. Leaves were exposed to light over various time intervals immediately after isolation and then kept in the dark. The results of these
experiments demonstrated that protonema regeneration is much less
dependent on light than bud formation and that the longer leaves have
been exposed to light the more buds are formed. Experiments in which
photosynthesis was selectively inhibited by sodium fluoride suggest that
this light effect is at least partly due to the production of substances