V.
DETERMINING FACTORS IN CELL
GROWTH
249
Problems of sex expression arise characteristically in dioecious plants
like the hemp or in plants where flowers of two different sexes are borne
at different levels. Heslop-Harrison (1957) and the Maheshwaris (1958)
have recently summarized the literature on the experimental modification of sex expression in plants.
That the balance which leads to the formation of male or female
flowers is controlled by the endogenous level of auxins has been suggested
by Heslop-Harrison (1957). The results of application of synthetic
growth regulators (Laibach and Kribben, 1951; Wittwer and Hillyer,
1954; Heslop-Harrison, 1956; J. and Y. Heslop-Harrisons, 1958) and
animal hormones (Löve and Löve, 1945) suggest that an increase in
auxin level in the vicinity of floral primordia sways the balance towards
the appearance of female flowers, in the sites where male flowers would
normally originate. However, attempts to induce male flowers in the
location of female flowers by the application of antiauxins like triiodobenzoic acid (Heslop-Harrisons, 1958) or maleic hydrazide (Naylor
and Davies, 1950) have been unsuccessful.
These cases have been cited here merely to point out how far we still
are from a full interpretation of these events in causal terms. For much
recent information on the effect of miscellaneous growth regulators
upon the incidence of flowering, reference may be made to the various
chapters of Thotoperiodism and Related Phenomena in Plants and
Animals', edited by the late Dr. Withrow (1959). However, until the
effects obtained by these often arbitrarily selefited synthetic substances
can be localized, both in the metabolic and morphogenetic processes
that they affect, their interpretation is almost as elusive as that of the
flowering response itself!
Thus many problems of the physiological interpretation of morphogenesis concern, in large part, the recognition of centres of activity in
growth and the determination of the stimuli that control whether cells,
which are inherently able to grow, do so by division and/or by enlargement, or indeed, have growth suppressed altogether. For some further
light on these questions, reference may now be made to some contrasted
problems of unorganized and organized growth, and especially to considerations which determine how the one may give rise to the other.
E. Unorganized Versus Organized Growth
The first point is a subtle one, namely that if cells are to give rise to
organized structures they seem to profit in some way by escape from the
restrictions imposed by their being present as part of a preformed, large
tissue mass. This restriction may be physical, or may involve some, as
DETERMINING FACTORS IN CELL
GROWTH
249
Problems of sex expression arise characteristically in dioecious plants
like the hemp or in plants where flowers of two different sexes are borne
at different levels. Heslop-Harrison (1957) and the Maheshwaris (1958)
have recently summarized the literature on the experimental modification of sex expression in plants.
That the balance which leads to the formation of male or female
flowers is controlled by the endogenous level of auxins has been suggested
by Heslop-Harrison (1957). The results of application of synthetic
growth regulators (Laibach and Kribben, 1951; Wittwer and Hillyer,
1954; Heslop-Harrison, 1956; J. and Y. Heslop-Harrisons, 1958) and
animal hormones (Löve and Löve, 1945) suggest that an increase in
auxin level in the vicinity of floral primordia sways the balance towards
the appearance of female flowers, in the sites where male flowers would
normally originate. However, attempts to induce male flowers in the
location of female flowers by the application of antiauxins like triiodobenzoic acid (Heslop-Harrisons, 1958) or maleic hydrazide (Naylor
and Davies, 1950) have been unsuccessful.
These cases have been cited here merely to point out how far we still
are from a full interpretation of these events in causal terms. For much
recent information on the effect of miscellaneous growth regulators
upon the incidence of flowering, reference may be made to the various
chapters of Thotoperiodism and Related Phenomena in Plants and
Animals', edited by the late Dr. Withrow (1959). However, until the
effects obtained by these often arbitrarily selefited synthetic substances
can be localized, both in the metabolic and morphogenetic processes
that they affect, their interpretation is almost as elusive as that of the
flowering response itself!
Thus many problems of the physiological interpretation of morphogenesis concern, in large part, the recognition of centres of activity in
growth and the determination of the stimuli that control whether cells,
which are inherently able to grow, do so by division and/or by enlargement, or indeed, have growth suppressed altogether. For some further
light on these questions, reference may now be made to some contrasted
problems of unorganized and organized growth, and especially to considerations which determine how the one may give rise to the other.
E. Unorganized Versus Organized Growth
The first point is a subtle one, namely that if cells are to give rise to
organized structures they seem to profit in some way by escape from the
restrictions imposed by their being present as part of a preformed, large
tissue mass. This restriction may be physical, or may involve some, as