140
LUISE STANGE
from the meristem these substances are available for new growth processes in the permanent cells. This opinion goes back to Goebel (1902,
1905, 1908), who assumed that themeristems act as 'attraction centres'
for building material and that new growth centres arise where building
material is accumulated. The polar arrangement of regenerates at places
where the transport of assimilation products to the meristems is interrupted, was taken as support for this hypothesis. Later investigators
(e.g. Linsbauer, 1926) assumed that special substances, but not necessarily building material, synthesized in the permanent cells might be
responsible for regeneration. (2) The growth functions of the permanent
cells are inhibited by substances produced in the meristems and transmitted to the permanent cells. As an analogy to the ideas about the
correlations between apical and lateral buds (Section II), it was assumed
that auxin might be the factor responsible for the growth inhibition of
mature cells. Regardless of the origin and direction of transport of the
hypothetical substances responsible for the growth inhibition of mature
cells, an additional explanation must be given for the fact that the cells
producing the substances do not react in the same way as the cells to
which the substances are transported. One must assume either different
sensitivities of the different cells or the existence of mechanisms of
active transport leading to different concentrations of the substances in
question in the different cells. The directed flow of substances may be
caused by chemical reactions.
Today no decision is possible between the two general ideas about the
nature of correlations. The following observation has been taken as
support of the first hypothesis: regenerates in isolated parts of the
plant, which inhibit regeneration in other cells, are at the same time
promoted by these cells. It can be seen in Table V that, in Splachnum,
the tissue of stem segment produces more regenerative protonema when
a leaf is attached to it, which for its part forms regenerates only after
being detached from the stem tissue. In Riella (Table VI) the largest
fragments have the lowest number of regenerates per unit area, due to
inhibiting correlations between the cells (cf. Section III, B). At the
same time the regenerates from the largest fragments have the greatest
size due to promotion by the inhibited cells. However, there is no proof
that the inhibiting and promoting correlations are identical. It has been
argued from experiments in higher plants, in which isolated leaves were
able to regenerate in the dark, that an accumulation of assimilation
products can not be the cause of regeneration (Behre, 1929). In Riella,
likewise, fragments kept in the dark after isolation produce regenerates.
But the interruption of photosynthesis does not mean that no substances are produced in the cells. In intact plants, growth of the apical
meristem also continues in the dark for several days, presumably at the
LUISE STANGE
from the meristem these substances are available for new growth processes in the permanent cells. This opinion goes back to Goebel (1902,
1905, 1908), who assumed that themeristems act as 'attraction centres'
for building material and that new growth centres arise where building
material is accumulated. The polar arrangement of regenerates at places
where the transport of assimilation products to the meristems is interrupted, was taken as support for this hypothesis. Later investigators
(e.g. Linsbauer, 1926) assumed that special substances, but not necessarily building material, synthesized in the permanent cells might be
responsible for regeneration. (2) The growth functions of the permanent
cells are inhibited by substances produced in the meristems and transmitted to the permanent cells. As an analogy to the ideas about the
correlations between apical and lateral buds (Section II), it was assumed
that auxin might be the factor responsible for the growth inhibition of
mature cells. Regardless of the origin and direction of transport of the
hypothetical substances responsible for the growth inhibition of mature
cells, an additional explanation must be given for the fact that the cells
producing the substances do not react in the same way as the cells to
which the substances are transported. One must assume either different
sensitivities of the different cells or the existence of mechanisms of
active transport leading to different concentrations of the substances in
question in the different cells. The directed flow of substances may be
caused by chemical reactions.
Today no decision is possible between the two general ideas about the
nature of correlations. The following observation has been taken as
support of the first hypothesis: regenerates in isolated parts of the
plant, which inhibit regeneration in other cells, are at the same time
promoted by these cells. It can be seen in Table V that, in Splachnum,
the tissue of stem segment produces more regenerative protonema when
a leaf is attached to it, which for its part forms regenerates only after
being detached from the stem tissue. In Riella (Table VI) the largest
fragments have the lowest number of regenerates per unit area, due to
inhibiting correlations between the cells (cf. Section III, B). At the
same time the regenerates from the largest fragments have the greatest
size due to promotion by the inhibited cells. However, there is no proof
that the inhibiting and promoting correlations are identical. It has been
argued from experiments in higher plants, in which isolated leaves were
able to regenerate in the dark, that an accumulation of assimilation
products can not be the cause of regeneration (Behre, 1929). In Riella,
likewise, fragments kept in the dark after isolation produce regenerates.
But the interruption of photosynthesis does not mean that no substances are produced in the cells. In intact plants, growth of the apical
meristem also continues in the dark for several days, presumably at the