H E T E R O B L A S T I C D E V E L O P M E N T IN P L A N T S
159
ity for cell multiplication in vitro decreased during reproductive and
senile stages.
Trippi made no mention of the preparation and continued growth of
subcultures of the original tissues. More extensive investigations along
these lines were undertaken by Stoutemyer and Britt (1963, 1965) who
compared the behavior of tissue cultures from English and Algerian ivy
in different growth phases. In English ivy cultures from the juvenile
phase had consistently greater growth rates in subcultures maintained
over a period of two years. In Algerian ivy the differences were even
greater in that subcultures could be prepared from the tissues from
juvenile phases, but not from adult phases.
2. Aging of Meristems
Stable modifications of the kind discussed above have been treated as
evidence of aging or maturation of the apical meristems. Thus, Robbins
(1957a) suggested as a working hypothesis that juvenility corresponds
to an unstable metabolic state of the meristem, which passes through a
series of steps to a relatively stable metabolic state characteristic of the
adult meristem. He also considered that the steady state of the adult
might be upset in the direction of the unstable metabolism of the
juvenile by cold, X-rays, products from the juvenile, the formation of
adventitious meristems, and by the formation of zygotes or of asexual
embryos. This view was strongly supported by Schaffalitzky de Muckadell (1959) on the basis of his own work on woody plants. The concept
of apical aging has also been accepted by Habermann (1962) and
Trippi (1964).
a. Apical Ontogeny. The primary enlargement of the apical meristem
and its role in primary heteroblastic development has already been
discussed. This size-structure correlation can now be regarded as one
of the basic principles of plant ontogeny. But the occurrence of other
significant changes in the apex is more debatable.
Various ontogenetic changes in the cytohistological zonation of the
shoot apex have been described but except at the time of floral initiation,
the differences, although evidence of some modification of apical activity,
do not appear to be very profound. It is only recently that detailed
studies have been made of metabolic changes in the shoot apex (Teltscherovâ and Krekule, 1966), but as with the anatomical investigations,
these studies have been concerned mainly with the transition from the
vegetative to the reproductive condition and although important add
little to our knowledge of heteroblastic development. In fact, the most
recent and comprehensive symposium on the anatomical and physiological differentiation of apical meristems (Prat, 1966) furnishes no evidence
of any role of apical differentiation in heteroblastic development.
159
ity for cell multiplication in vitro decreased during reproductive and
senile stages.
Trippi made no mention of the preparation and continued growth of
subcultures of the original tissues. More extensive investigations along
these lines were undertaken by Stoutemyer and Britt (1963, 1965) who
compared the behavior of tissue cultures from English and Algerian ivy
in different growth phases. In English ivy cultures from the juvenile
phase had consistently greater growth rates in subcultures maintained
over a period of two years. In Algerian ivy the differences were even
greater in that subcultures could be prepared from the tissues from
juvenile phases, but not from adult phases.
2. Aging of Meristems
Stable modifications of the kind discussed above have been treated as
evidence of aging or maturation of the apical meristems. Thus, Robbins
(1957a) suggested as a working hypothesis that juvenility corresponds
to an unstable metabolic state of the meristem, which passes through a
series of steps to a relatively stable metabolic state characteristic of the
adult meristem. He also considered that the steady state of the adult
might be upset in the direction of the unstable metabolism of the
juvenile by cold, X-rays, products from the juvenile, the formation of
adventitious meristems, and by the formation of zygotes or of asexual
embryos. This view was strongly supported by Schaffalitzky de Muckadell (1959) on the basis of his own work on woody plants. The concept
of apical aging has also been accepted by Habermann (1962) and
Trippi (1964).
a. Apical Ontogeny. The primary enlargement of the apical meristem
and its role in primary heteroblastic development has already been
discussed. This size-structure correlation can now be regarded as one
of the basic principles of plant ontogeny. But the occurrence of other
significant changes in the apex is more debatable.
Various ontogenetic changes in the cytohistological zonation of the
shoot apex have been described but except at the time of floral initiation,
the differences, although evidence of some modification of apical activity,
do not appear to be very profound. It is only recently that detailed
studies have been made of metabolic changes in the shoot apex (Teltscherovâ and Krekule, 1966), but as with the anatomical investigations,
these studies have been concerned mainly with the transition from the
vegetative to the reproductive condition and although important add
little to our knowledge of heteroblastic development. In fact, the most
recent and comprehensive symposium on the anatomical and physiological differentiation of apical meristems (Prat, 1966) furnishes no evidence
of any role of apical differentiation in heteroblastic development.