V. DETERMINING FACTORS IN
CELL GROWTH
197
growth induction, can therefore shed light upon the regulatory control
over cell division.
To a limited extent, as shown by the phenomena of wound healing,
injuries of one sort or another may induce in the neighbouring cells
responses in which a limited recrudescence of cell division is a prominent
feature. A classical example is the formation of a wound periderm or
phellogen, at the cut surface of the cells of a potato tuber. Indeed, in
the course of leaf fall and abscision, mature cells are brought again
to a state of active growth by division. Long ago, Haberlandt (1922)
conceived that the renewal of cell division consequent upon the wound
reaction was the result of a special hormone, which he called the wound
hormone, and for a long time this response was identified with this
hypothetical substance. In an attempt to induce additional embryos
based on his theory, he pin-pricked or gently squeezed Oenothera
ovules and, surprisingly enough, obtained two embryos in one ovule
(Haberlandt, 1921). These experiments of Haberlandt seem not to have
been repeated successfully to this day. In the late 1930's publications from the California Institute of Technology (e.g. English and
Bonner, 1937; English et al., 1939) contained claims identifying this
wound substance called traumatin, and assigning to it a definite
chemical constitution (l-decene-l,10-dicarboxylic acid). However, with
the lapse of time, it is clear that this particular molecule, to which the
California group attributed the ability to stimulate and control cell
division, is not generally effective in this way. While it is clear, therefore,
that there must be some regulatory control of cell division in the plant
body, the means by which this is achieved have remained obscure until
relatively recently.
In an attempt to stimulate cell division and growth in isolated plant
tissue cultures, a great variety of substances and extracts have been
tried (White, 1943, 1954; Gautheret, 1942, 1959; Van Overbeek et al.,
1944 and references there cited). Without attempting a full review of
this now active field of work, the general status of the subject will be
summarized by reference only to a few main lines of investigation. One
of these lines is associated with the work done in this laboratory on the
chemical induction of growth in plant tissue cultures, notably of the
carrot root; another relates to the studies of Skoog and his associates on
the physiology and biochemistry of growth induction in the tissue of
tobacco pith; and a third concerns knowledge that is to be gained by the
understanding of the stimuli involved in tumour formation such as that
which can be induced by the crown gall organism, as investigated by
Braun. While this selection may leave many worthy investigations
uncited, the points that are applicable to the rest of this discussion can
adequately be developed in this way.
CELL GROWTH
197
growth induction, can therefore shed light upon the regulatory control
over cell division.
To a limited extent, as shown by the phenomena of wound healing,
injuries of one sort or another may induce in the neighbouring cells
responses in which a limited recrudescence of cell division is a prominent
feature. A classical example is the formation of a wound periderm or
phellogen, at the cut surface of the cells of a potato tuber. Indeed, in
the course of leaf fall and abscision, mature cells are brought again
to a state of active growth by division. Long ago, Haberlandt (1922)
conceived that the renewal of cell division consequent upon the wound
reaction was the result of a special hormone, which he called the wound
hormone, and for a long time this response was identified with this
hypothetical substance. In an attempt to induce additional embryos
based on his theory, he pin-pricked or gently squeezed Oenothera
ovules and, surprisingly enough, obtained two embryos in one ovule
(Haberlandt, 1921). These experiments of Haberlandt seem not to have
been repeated successfully to this day. In the late 1930's publications from the California Institute of Technology (e.g. English and
Bonner, 1937; English et al., 1939) contained claims identifying this
wound substance called traumatin, and assigning to it a definite
chemical constitution (l-decene-l,10-dicarboxylic acid). However, with
the lapse of time, it is clear that this particular molecule, to which the
California group attributed the ability to stimulate and control cell
division, is not generally effective in this way. While it is clear, therefore,
that there must be some regulatory control of cell division in the plant
body, the means by which this is achieved have remained obscure until
relatively recently.
In an attempt to stimulate cell division and growth in isolated plant
tissue cultures, a great variety of substances and extracts have been
tried (White, 1943, 1954; Gautheret, 1942, 1959; Van Overbeek et al.,
1944 and references there cited). Without attempting a full review of
this now active field of work, the general status of the subject will be
summarized by reference only to a few main lines of investigation. One
of these lines is associated with the work done in this laboratory on the
chemical induction of growth in plant tissue cultures, notably of the
carrot root; another relates to the studies of Skoog and his associates on
the physiology and biochemistry of growth induction in the tissue of
tobacco pith; and a third concerns knowledge that is to be gained by the
understanding of the stimuli involved in tumour formation such as that
which can be induced by the crown gall organism, as investigated by
Braun. While this selection may leave many worthy investigations
uncited, the points that are applicable to the rest of this discussion can
adequately be developed in this way.