256
F. C. STEWARD AND Η. Y. MOHAN
RAM
manner in which this is expressed—by cell multiplication, enlargement,
or even by differentiation—becomes a problem of chemical growth
regulation. An array of regulatory substances, natural and synthetic,
may intervene to control or modulate these events within limits that
are set by the genetic machinery.
In plants, at least, the range within which growth and development
may be so modulated is wide—and it is the cardinal problem of morphogenesis to recognize the regulatory substances and asymmetric stimuli
by which these variations are determined. In short, it is as futile to leave
the 'non-genetic' controlling factors out of account as it would be, at the
other extreme, to explain all the facts of morphogenesis in terms of
known kinds of chemical growth factors, regulators or stimuli, without
regard to the genetically imprinted machinery which controls the system
which is, in turn, responsive to the agents in question. One needs,
therefore, a proper blend of the genetic controls on the one hand and
what have been called 'epigenetic factors or stimuli' on the other
(Waddington, 1957).
One may paraphrase this distinction to mean on the one hand 'nature',
in the accepted genetic sense of characteristics that are hereditarily or
evolutionarily pre-determined, wholly or in part, by the pentose nuclei
acid of the nucleus, and, on the other hand, 'nurture' in the sense of this
review. Nurture here implies that specialized complement of chemical
growth factors and stimuli that are a part of the over-all nutrition of
organs or embryos, and which act, over and above ordinary nutrients,
to control cell growth and development, within the limits of response
which are set by their genetic make-up.
This increasingly conspicuous complement of factors and formative
substances, notably to be found in endosperms, represents the physical
embodiment of what J. T. Bonner* called the 'continuing chemical
conversations between cytoplasm and nucleus', which he postulated to
account for the facts of development and morphogenesis. They may also
represent a part of the complex system which Waddington visualized
as connecting his 'epigenetic landscape' (representing the variations
that occur during development) to the fixed complement of genetic
determinants.
The purpose of this chapter will have been served if it has become
apparent that the problems of plant morphology and morphogenesis
may now be approached, with some hope of success, by experimental
techniques which stem from the culture methods through which one
may determine the requirements for growth of particular cells—multi* Quoted from a lecture entitled 'Morphogenesis in lower organisms' delivered by Professor J. T. Bonner in a symposium of the A.A.A.S., Washington, D.C., on December 30,
1958.
F. C. STEWARD AND Η. Y. MOHAN
RAM
manner in which this is expressed—by cell multiplication, enlargement,
or even by differentiation—becomes a problem of chemical growth
regulation. An array of regulatory substances, natural and synthetic,
may intervene to control or modulate these events within limits that
are set by the genetic machinery.
In plants, at least, the range within which growth and development
may be so modulated is wide—and it is the cardinal problem of morphogenesis to recognize the regulatory substances and asymmetric stimuli
by which these variations are determined. In short, it is as futile to leave
the 'non-genetic' controlling factors out of account as it would be, at the
other extreme, to explain all the facts of morphogenesis in terms of
known kinds of chemical growth factors, regulators or stimuli, without
regard to the genetically imprinted machinery which controls the system
which is, in turn, responsive to the agents in question. One needs,
therefore, a proper blend of the genetic controls on the one hand and
what have been called 'epigenetic factors or stimuli' on the other
(Waddington, 1957).
One may paraphrase this distinction to mean on the one hand 'nature',
in the accepted genetic sense of characteristics that are hereditarily or
evolutionarily pre-determined, wholly or in part, by the pentose nuclei
acid of the nucleus, and, on the other hand, 'nurture' in the sense of this
review. Nurture here implies that specialized complement of chemical
growth factors and stimuli that are a part of the over-all nutrition of
organs or embryos, and which act, over and above ordinary nutrients,
to control cell growth and development, within the limits of response
which are set by their genetic make-up.
This increasingly conspicuous complement of factors and formative
substances, notably to be found in endosperms, represents the physical
embodiment of what J. T. Bonner* called the 'continuing chemical
conversations between cytoplasm and nucleus', which he postulated to
account for the facts of development and morphogenesis. They may also
represent a part of the complex system which Waddington visualized
as connecting his 'epigenetic landscape' (representing the variations
that occur during development) to the fixed complement of genetic
determinants.
The purpose of this chapter will have been served if it has become
apparent that the problems of plant morphology and morphogenesis
may now be approached, with some hope of success, by experimental
techniques which stem from the culture methods through which one
may determine the requirements for growth of particular cells—multi* Quoted from a lecture entitled 'Morphogenesis in lower organisms' delivered by Professor J. T. Bonner in a symposium of the A.A.A.S., Washington, D.C., on December 30,
1958.