158
A. ALLSOPP
example, cuttings from adult parts of the ivy, Hedera helix, normally
retain all their distinctive characteristics on rooting and further growth.
Schaff alitzky de Muckadell (1959) described many similar examples of
the retention of characteristics in cuttings taken from adult parts of
various forest trees. Even more convincing evidence of stability in
meristems is revealed by topophysis (Molisch, 1929) in which the behavior of an isolated plant part is determined by its position on the
parent shoot. In a recently described example (Bancilhon et al, 1963),
lateral branches of the orthotropic main axis of species of Phyllanthus
continued their plagiotropic growth when rooted as cuttings.
Grafting has been principally studied with the object of promoting
earlier maturation of scions of commercially valuable species. In his
review of this work Sax (1962) concluded that there is still no conclusive evidence that the grafting or budding of juvenile shoots on mature
parts hastens their flowering. In numerous experiments with various
hardwood species, Schaffalitzky de Muckadell (1959) convincingly demonstrated the persistence of juvenile and adult characteristics in the
grafted scions. Some results obtained with grafts by other workers are
considered below.
b. Differences in Growth Vigor. Several authors, e.g., Schaffalitzky de
Muckadell (1959) have drawn attention to the greater growth vigor of
juvenile stages. In beech, Fagus sylvatica, the difference persisted in
grafted scions. In a recent investigation, Trippi (1963a) observed that
the relative annual growth of juvenile and adult branches varies according to the species. Thus, in Tilia parviflora, Robinia pseudoacacia, and
Castanea vulgaris, the juvenile branches had more vigorous growth,
whereas in Ilex aquifolium and Aesculus hippocastanum adult branches
had greater growth.
In a number of cultivated plants, it has been found that various
devices for reducing the growth rate can result in earlier flowering,
provided the plants are already of sufficient size. The methods adopted
include the use of dwarfing rootstocks, girdling the bark, inverting a
ring of bark, training the main axes or branches in a horizontal position,
or even tying a knot in the stem (Sax, 1962).
c. Evidence from Tissue Cultures. Reference has been made above to
the greater rooting capacity and, on the whole, greater growth vigor of
the juvenile stages. These differences add interest to observations on the
culture of isolated tissues from these different regions. Trippi (1963b,c)
studied tissues taken from juvenile and adult zones of Aesculus and
Castanea, and from juvenile and adult plants of Castanea and Robinia.
It was found that the proliferative capacity depends on the species. In
Castanea, there was a greater proliferation of tissues from the juvenile
zone; in Aesculus, the reverse. In both Castanea and Robinia the capac-
A. ALLSOPP
example, cuttings from adult parts of the ivy, Hedera helix, normally
retain all their distinctive characteristics on rooting and further growth.
Schaff alitzky de Muckadell (1959) described many similar examples of
the retention of characteristics in cuttings taken from adult parts of
various forest trees. Even more convincing evidence of stability in
meristems is revealed by topophysis (Molisch, 1929) in which the behavior of an isolated plant part is determined by its position on the
parent shoot. In a recently described example (Bancilhon et al, 1963),
lateral branches of the orthotropic main axis of species of Phyllanthus
continued their plagiotropic growth when rooted as cuttings.
Grafting has been principally studied with the object of promoting
earlier maturation of scions of commercially valuable species. In his
review of this work Sax (1962) concluded that there is still no conclusive evidence that the grafting or budding of juvenile shoots on mature
parts hastens their flowering. In numerous experiments with various
hardwood species, Schaffalitzky de Muckadell (1959) convincingly demonstrated the persistence of juvenile and adult characteristics in the
grafted scions. Some results obtained with grafts by other workers are
considered below.
b. Differences in Growth Vigor. Several authors, e.g., Schaffalitzky de
Muckadell (1959) have drawn attention to the greater growth vigor of
juvenile stages. In beech, Fagus sylvatica, the difference persisted in
grafted scions. In a recent investigation, Trippi (1963a) observed that
the relative annual growth of juvenile and adult branches varies according to the species. Thus, in Tilia parviflora, Robinia pseudoacacia, and
Castanea vulgaris, the juvenile branches had more vigorous growth,
whereas in Ilex aquifolium and Aesculus hippocastanum adult branches
had greater growth.
In a number of cultivated plants, it has been found that various
devices for reducing the growth rate can result in earlier flowering,
provided the plants are already of sufficient size. The methods adopted
include the use of dwarfing rootstocks, girdling the bark, inverting a
ring of bark, training the main axes or branches in a horizontal position,
or even tying a knot in the stem (Sax, 1962).
c. Evidence from Tissue Cultures. Reference has been made above to
the greater rooting capacity and, on the whole, greater growth vigor of
the juvenile stages. These differences add interest to observations on the
culture of isolated tissues from these different regions. Trippi (1963b,c)
studied tissues taken from juvenile and adult zones of Aesculus and
Castanea, and from juvenile and adult plants of Castanea and Robinia.
It was found that the proliferative capacity depends on the species. In
Castanea, there was a greater proliferation of tissues from the juvenile
zone; in Aesculus, the reverse. In both Castanea and Robinia the capac-