126
LUISE STANGE
number of protonemata per leaf is a useful criterion for the ability of the
leaf cells to regenerate. The number of protonemata may be different
from the number of dividing cells. I t has been shown that correlative
factors are operative within the isolated leaf (cf. Section I I I , B) and
these correlations may be different in leaves of different age. On the
other hand, embryonization as a consequence of physiological isolation
from a meristem by growth has been demonstrated as a widely distributed process in normal development (Bünning, 1953). In Splachnum
ampullaceum (von Maltzahn and MacNutt, 1958) successive leaves from
the base towards the apex showed steadily increasing numbers of regenerates. The relative number of regenerates in successive leaves did
not change with the regeneration time. When the regenerative behaviour
of young and older gametophores was compared, leaves from younger
gametophores showed consistently a much higher number of regenerates
than leaves from older plants, the gradient for successive leaves being
realized in both cases.
In Biella, tissues of increasing age can be isolated by cutting fragments out of the wing proceeding from the apex to the base (Stange,
1957). The time of appearance of regenerative cauloids and rhizoids
showed a clear dependence on the age of the cells. This dependence
became especially clear in an investigation of the changes in the cell
preceding the first regenerative division. In Fig. 4 quantitative results
are presented for the increase in nucleolar size in isolated tissue of
different age. This comparison is achieved by cutting out fragments in
the apical and in the basal region of the wing and by measuring the
diameter of round nucleoli at different time intervals after isolation.
I t is clear from this figure that in the adaxial zone of the fragment the
rates of nucleolar increase are different in younger and older cells. The
final size of the nucleolus of about 5 μ is reached earlier in younger cells
(after 24 h) than in older cells (after 48 h). A nucleolar diameter of 5 μ is
characteristic for meristematic cells (Schult, 1962). (The nucleolar size
in the other zones of the fragments is not of interest in this connexion,
since it is influenced by the correlations between the cells within the
fragment (cf. Section III, B).) I t can be seen from the Figure that there
are differences in the size of the nucleolus in young and old cells previous
to isolation. This may contribute to the differences in the time required
to reach the final size of the nucleolus.
Figure 3 includes results of another change in the cells during embryonization, namely the decrease in chloroplast size and the increase in
chloroplast number in detached leaves of Splachnum taken from the
apex and the base of the plant (MacNutt and von Maltzahn, 1960). The
first changes in the cells of the younger and older isolated leaves are
observed at about the same time after isolation. But differences between
LUISE STANGE
number of protonemata per leaf is a useful criterion for the ability of the
leaf cells to regenerate. The number of protonemata may be different
from the number of dividing cells. I t has been shown that correlative
factors are operative within the isolated leaf (cf. Section I I I , B) and
these correlations may be different in leaves of different age. On the
other hand, embryonization as a consequence of physiological isolation
from a meristem by growth has been demonstrated as a widely distributed process in normal development (Bünning, 1953). In Splachnum
ampullaceum (von Maltzahn and MacNutt, 1958) successive leaves from
the base towards the apex showed steadily increasing numbers of regenerates. The relative number of regenerates in successive leaves did
not change with the regeneration time. When the regenerative behaviour
of young and older gametophores was compared, leaves from younger
gametophores showed consistently a much higher number of regenerates
than leaves from older plants, the gradient for successive leaves being
realized in both cases.
In Biella, tissues of increasing age can be isolated by cutting fragments out of the wing proceeding from the apex to the base (Stange,
1957). The time of appearance of regenerative cauloids and rhizoids
showed a clear dependence on the age of the cells. This dependence
became especially clear in an investigation of the changes in the cell
preceding the first regenerative division. In Fig. 4 quantitative results
are presented for the increase in nucleolar size in isolated tissue of
different age. This comparison is achieved by cutting out fragments in
the apical and in the basal region of the wing and by measuring the
diameter of round nucleoli at different time intervals after isolation.
I t is clear from this figure that in the adaxial zone of the fragment the
rates of nucleolar increase are different in younger and older cells. The
final size of the nucleolus of about 5 μ is reached earlier in younger cells
(after 24 h) than in older cells (after 48 h). A nucleolar diameter of 5 μ is
characteristic for meristematic cells (Schult, 1962). (The nucleolar size
in the other zones of the fragments is not of interest in this connexion,
since it is influenced by the correlations between the cells within the
fragment (cf. Section III, B).) I t can be seen from the Figure that there
are differences in the size of the nucleolus in young and old cells previous
to isolation. This may contribute to the differences in the time required
to reach the final size of the nucleolus.
Figure 3 includes results of another change in the cells during embryonization, namely the decrease in chloroplast size and the increase in
chloroplast number in detached leaves of Splachnum taken from the
apex and the base of the plant (MacNutt and von Maltzahn, 1960). The
first changes in the cells of the younger and older isolated leaves are
observed at about the same time after isolation. But differences between