V.
DETERMINING FACTORS IN CELL GROWTH
257
plying or enlarging in an unorganized or organized way—which are
subject to regulatory controls of substances, or systems, which may soon
be completely defined. In this way the behaviour of cells in the plant
body becomes a function of the milieu in which they occur.
It is a feature of modern biology to attempt to reduce everything to
the molecular level. The concept of 'molecular biology' expresses the
perhaps too confident philosophy that genes and enzymes determine the
molecular configuration of specific proteins and complex molecules, and
that these in turn regulate and determine the nature and growth of the
organism. It does not detract from the dramatic gains that have been
made by these means in recent years to recognize that they have contributed much to our ideas of metabolism and relatively little to the
problems of organization. Growth and morphogenesis can only be fully
interpreted at higher levels of organization than the molecular.
If this review has merit, it will have indicated that an array of
regulatory substances, furnished by special tissues (e.g. the endosperm),
or fluids secreted from localized centres of stimuli (e.g. in the
apices of shoot or root) may exercise control over the responses of cells
and that these controls over-ride the genetic effects. For the full
interpretation of these phenomena, one needs to look not solely to the
properties or structure of physiologically active compounds nor to single
or explicit reactions which they invoke, but also to the wqy cells—as
working, organized structures and as part of even larger organizations—
are modified during the course of their growth and development and by
their position. The problem now is to explain how such complex systems
as cells are so profoundly affected by such simple controlling agents, for
in no case has this been satisfactorily worked out. Nevertheless, from the
gains that have already been made, one may anticipate that a chemical
basis of morphogenesis will eventually emerge.
Acknowledgements
One of us (H.Y.M.R.) was the recipient of a Fulbright Travel Grant
and a Smith-Mundt Scholarship during part of his stay at Cornell
University, which made this collaboration possible.
Many of the views here expressed developed from experimental work
which was supported by grants to one of us (F.C.S.) from the National
Cancer Institute, National Institutes of Health, Department of Health,
Education, and Welfare, Bethesda, Maryland. This support is gratefully
acknowledged.
The authors also wish to thank Dr. Manasi Ram and Mrs. Marion
0. Mapes for help with the preparation of the manuscript and the
illustrations.
DETERMINING FACTORS IN CELL GROWTH
257
plying or enlarging in an unorganized or organized way—which are
subject to regulatory controls of substances, or systems, which may soon
be completely defined. In this way the behaviour of cells in the plant
body becomes a function of the milieu in which they occur.
It is a feature of modern biology to attempt to reduce everything to
the molecular level. The concept of 'molecular biology' expresses the
perhaps too confident philosophy that genes and enzymes determine the
molecular configuration of specific proteins and complex molecules, and
that these in turn regulate and determine the nature and growth of the
organism. It does not detract from the dramatic gains that have been
made by these means in recent years to recognize that they have contributed much to our ideas of metabolism and relatively little to the
problems of organization. Growth and morphogenesis can only be fully
interpreted at higher levels of organization than the molecular.
If this review has merit, it will have indicated that an array of
regulatory substances, furnished by special tissues (e.g. the endosperm),
or fluids secreted from localized centres of stimuli (e.g. in the
apices of shoot or root) may exercise control over the responses of cells
and that these controls over-ride the genetic effects. For the full
interpretation of these phenomena, one needs to look not solely to the
properties or structure of physiologically active compounds nor to single
or explicit reactions which they invoke, but also to the wqy cells—as
working, organized structures and as part of even larger organizations—
are modified during the course of their growth and development and by
their position. The problem now is to explain how such complex systems
as cells are so profoundly affected by such simple controlling agents, for
in no case has this been satisfactorily worked out. Nevertheless, from the
gains that have already been made, one may anticipate that a chemical
basis of morphogenesis will eventually emerge.
Acknowledgements
One of us (H.Y.M.R.) was the recipient of a Fulbright Travel Grant
and a Smith-Mundt Scholarship during part of his stay at Cornell
University, which made this collaboration possible.
Many of the views here expressed developed from experimental work
which was supported by grants to one of us (F.C.S.) from the National
Cancer Institute, National Institutes of Health, Department of Health,
Education, and Welfare, Bethesda, Maryland. This support is gratefully
acknowledged.
The authors also wish to thank Dr. Manasi Ram and Mrs. Marion
0. Mapes for help with the preparation of the manuscript and the
illustrations.