REGENERATION IN LOWER PLANTS
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'division of labour' on the functional level. In multicellular organisms
this 'division of labour' manifests itself very often most strikingly in a
local separation of cells (or a cell), which undergo growth and division
(meristematic tissue), and other cells, which have ceased to do so but
have taken over other important functions for the whole individual
(permanent tissue). This process of differentiation between cells is
brought about by correlations existing between the cells of a multicellular organism. Under optimal conditions, the cells of single-cellular
organisms run continuously through the cycle of growth and division.
This is true also for the meristematic cells of a multicellular organism. In
the cells of a multicellular organism that no longer divide, this cycle must
be interrupted at some point, and this interruption must be caused by
specific correlations between the cells. The sequence of metabolic processes in the always continually repeated cycle is turned aside and the
cycle cannot be closed. Instead, the cells pursue different courses toward
functional specialization in dependence on their environment and their
relation to other cells. Embryonization is the process in which the cell
gives up its special functional position and enters again the cycle of embryonic functions. Like the process of differentiation, the process of
embryonization is characterized by fundamental switches of metabolic
activities. By studying the conditions for the induction of embryonization,
information can be obtained about the nature of correlations operating
in differentiation. A complete knowledge of the sequence of changes in
the cells during embryonization may allow conclusions about the point at
which the cell cycle is interrupted, i.e. about the point of attack of the
correlations in question. Furthermore, investigations on this type of
regeneration throw light on the developmental potencies of specialized
cells and thus on the nature of their state of specialization.
In lower plants, with their simpler organization, regeneration by way
of embryonization is very common. Therefore, they are specially
suitable to a study of the phenomena involved. Research in this field
has followed mainly three different lines, (a) What changes occur in the
permanent cells during embryonization? (6) Where in the regenerating
part of the plant do the cells become embryonic again and which factors
determine the location of regenerates? (c) Which factors are responsible
for the induction of embryonization? This is indirectly the question of
the nature of correlations between meristematic and permanent cells.
A. The Changes in the Cells during Embryonization
1. Structural and Metabolic Changes
The changes in permanent cells re-entering division and giving origin
to a regenerate have been described for several species. In studying the
117
'division of labour' on the functional level. In multicellular organisms
this 'division of labour' manifests itself very often most strikingly in a
local separation of cells (or a cell), which undergo growth and division
(meristematic tissue), and other cells, which have ceased to do so but
have taken over other important functions for the whole individual
(permanent tissue). This process of differentiation between cells is
brought about by correlations existing between the cells of a multicellular organism. Under optimal conditions, the cells of single-cellular
organisms run continuously through the cycle of growth and division.
This is true also for the meristematic cells of a multicellular organism. In
the cells of a multicellular organism that no longer divide, this cycle must
be interrupted at some point, and this interruption must be caused by
specific correlations between the cells. The sequence of metabolic processes in the always continually repeated cycle is turned aside and the
cycle cannot be closed. Instead, the cells pursue different courses toward
functional specialization in dependence on their environment and their
relation to other cells. Embryonization is the process in which the cell
gives up its special functional position and enters again the cycle of embryonic functions. Like the process of differentiation, the process of
embryonization is characterized by fundamental switches of metabolic
activities. By studying the conditions for the induction of embryonization,
information can be obtained about the nature of correlations operating
in differentiation. A complete knowledge of the sequence of changes in
the cells during embryonization may allow conclusions about the point at
which the cell cycle is interrupted, i.e. about the point of attack of the
correlations in question. Furthermore, investigations on this type of
regeneration throw light on the developmental potencies of specialized
cells and thus on the nature of their state of specialization.
In lower plants, with their simpler organization, regeneration by way
of embryonization is very common. Therefore, they are specially
suitable to a study of the phenomena involved. Research in this field
has followed mainly three different lines, (a) What changes occur in the
permanent cells during embryonization? (6) Where in the regenerating
part of the plant do the cells become embryonic again and which factors
determine the location of regenerates? (c) Which factors are responsible
for the induction of embryonization? This is indirectly the question of
the nature of correlations between meristematic and permanent cells.
A. The Changes in the Cells during Embryonization
1. Structural and Metabolic Changes
The changes in permanent cells re-entering division and giving origin
to a regenerate have been described for several species. In studying the