V.
DETERMINING FACTORS IN
CELL GROWTH
191
embryo sac itself also require interpretation and this growth, stemming
from the megaspore, whether at the expense of substances supplied
by the nucellus or other structures (integuments), has not been fully
duplicated in culture. Greater success has, however, attended the growth
of ovules, parts of ovules or whole ovaries in culture shortly after
pollination.
The most successful attempts recorded are the artificial culture of
nucellus (Ranga Swamy, 1958); or of ovules, 1-2 days after pollination,
by N. Maheshwari (1958), Sachar and Kapoor (1958), PoddubnajaArnoldi (1959), Ranga Swamy (1959); or of entire ovaries by Nitsch
(1951), Sachar and Baldev (1958), Sachar and Kanta (1958), N.
Maheshwari and Lai (1958); or of flowers by Jansen and Bonner (1949)
and Leopold and Scott (1952). Nevertheless, the isolation of a fertilized
egg from the embryo sac under aseptic conditions and without injury is
difficult, and even dissections of embryo sacs following gametic union to
study the subsequent events in culture, have been without success.
The capacity to produce the plant body does not, however, reside in
the zygote alone—indeed in the light of more recent work it may well
persist, even though suppressed, in almost any living cell of the entire
plant body. Cells, organs, and tissues removed from the plant body,
after they have already proceeded far in their development, can be
cultivated aseptically and in isolation by the now well known practices
of tissue and organ culture, and the factors which govern their manner
and rate of growth by cell division or by cell enlargement can be, and
have been, investigated. Out of this body of knowledge there now
emerge certain concepts of the requirements for the division of cells and
for their subsequent enlargement, and of factors which stimulate or
limit this growth. In large part, the purpose of this article is to survey
and recapitulate the essential requirements of cells for growth, and in
the light of these to re-examine problems of normal growth and
development. An objective will be to see the extent to which growth may
be interpreted as the unfolding of characteristics which may be regarded
as innate in the growing system and how far it requires interpretation in
terms of special nutrition or nurture. In short, this review will deal with
the borderline area between cell physiology and nutrition on the one
hand and morphogenesis on the other.
The fertilized egg gives rise to an organized embryo by characteristic
sequences of events (see Schnarf, 1931; Johansen, 1950; Maheshwari,
1950; Wardlaw, 1955). The essential nutriment which the developing
embryo receives derives from the parent sporophyte, especially from
tissues around and within the embryo sac. However, the impressive
feature is that this is not furnished immediately to the embryo, but is
elaborated in a special manner as follows. By the familiar act of 'triple
DETERMINING FACTORS IN
CELL GROWTH
191
embryo sac itself also require interpretation and this growth, stemming
from the megaspore, whether at the expense of substances supplied
by the nucellus or other structures (integuments), has not been fully
duplicated in culture. Greater success has, however, attended the growth
of ovules, parts of ovules or whole ovaries in culture shortly after
pollination.
The most successful attempts recorded are the artificial culture of
nucellus (Ranga Swamy, 1958); or of ovules, 1-2 days after pollination,
by N. Maheshwari (1958), Sachar and Kapoor (1958), PoddubnajaArnoldi (1959), Ranga Swamy (1959); or of entire ovaries by Nitsch
(1951), Sachar and Baldev (1958), Sachar and Kanta (1958), N.
Maheshwari and Lai (1958); or of flowers by Jansen and Bonner (1949)
and Leopold and Scott (1952). Nevertheless, the isolation of a fertilized
egg from the embryo sac under aseptic conditions and without injury is
difficult, and even dissections of embryo sacs following gametic union to
study the subsequent events in culture, have been without success.
The capacity to produce the plant body does not, however, reside in
the zygote alone—indeed in the light of more recent work it may well
persist, even though suppressed, in almost any living cell of the entire
plant body. Cells, organs, and tissues removed from the plant body,
after they have already proceeded far in their development, can be
cultivated aseptically and in isolation by the now well known practices
of tissue and organ culture, and the factors which govern their manner
and rate of growth by cell division or by cell enlargement can be, and
have been, investigated. Out of this body of knowledge there now
emerge certain concepts of the requirements for the division of cells and
for their subsequent enlargement, and of factors which stimulate or
limit this growth. In large part, the purpose of this article is to survey
and recapitulate the essential requirements of cells for growth, and in
the light of these to re-examine problems of normal growth and
development. An objective will be to see the extent to which growth may
be interpreted as the unfolding of characteristics which may be regarded
as innate in the growing system and how far it requires interpretation in
terms of special nutrition or nurture. In short, this review will deal with
the borderline area between cell physiology and nutrition on the one
hand and morphogenesis on the other.
The fertilized egg gives rise to an organized embryo by characteristic
sequences of events (see Schnarf, 1931; Johansen, 1950; Maheshwari,
1950; Wardlaw, 1955). The essential nutriment which the developing
embryo receives derives from the parent sporophyte, especially from
tissues around and within the embryo sac. However, the impressive
feature is that this is not furnished immediately to the embryo, but is
elaborated in a special manner as follows. By the familiar act of 'triple