REGENERATION IN LOWER PLANTS
113
investigation of the mechanisms underlying the completely different
courses of differentiation in the two alternating generations.
II. Reactivation of Quiescent Embryonic Centres
When parts of a plant are isolated which do not possess an actively
growing meristem but latent buds or primordia, the latter will start to
grow and develop into new plants or organs. The new development can
originate either from already organized buds or only from small groups
of meristematic cells or even from a single, still embryonic, cell lying in
an area of mature cells (e.g. protonema-initials in some mosses). These
are cases of regeneration by unfolding of 'Anlagen' already present
(Bûnning, 1955). The critical step in this type of regeneration is the
reactivation of meristematic cells, which have been without developmental activity since their formation. As has been shown in many
investigations, they are, in the undisturbed development, under correlative inhibition caused by the presence of an actively growing
meristematic centre. Their further development after reactivation
usually follows the course of normal development. Only a few cases in
lower plants have been studied in this respect. Nevertheless, these
investigations have contributed to the discussion about the nature of
correlative inhibition of latent primordia by the actively growing apical
centre, the phenomenon of the so-called apical dominance.
In the moss Funaria hygrometrica the phenomenon of apical dominance has been studied by Sironval (1952). In plants with an intact apex
some lateral branches occasionally occurred but were always restricted
to the base of the gametophore. On the other hand, after decapitation of
the apex of gametophores, lateral buds grew out, mainly in the upper
part of the gametophore and to a lesser extent in its middle and basal
regions. Lateral buds also grew out from isolated segments of the stem
(cf. Ainsworth, 1956). Stem segments without a bud regenerated protonemà. The possible influence of the apex in the correlative inhibition of
lateral buds was examined also by MacQuarrie and von Maltzahn (1959)
in the moss Splachnum ampullaceum by comparing lateral bud behaviour
in decapitated and intact plants. The results were evaluated by calculating the percentage of branches per axil present in the plants. While
in intact plants the percentage of growing lateral branches varied between 0 and 29% (depending on the different experiments), in decapitated plants 57-97% buds were reactivated. Removal of the apical
region, therefore, resulted in the removal of influences which inhibited
the activity of lateral buds. It was also observed that in later stages of
development of intact gametophores a considerable amount of lateral
113
investigation of the mechanisms underlying the completely different
courses of differentiation in the two alternating generations.
II. Reactivation of Quiescent Embryonic Centres
When parts of a plant are isolated which do not possess an actively
growing meristem but latent buds or primordia, the latter will start to
grow and develop into new plants or organs. The new development can
originate either from already organized buds or only from small groups
of meristematic cells or even from a single, still embryonic, cell lying in
an area of mature cells (e.g. protonema-initials in some mosses). These
are cases of regeneration by unfolding of 'Anlagen' already present
(Bûnning, 1955). The critical step in this type of regeneration is the
reactivation of meristematic cells, which have been without developmental activity since their formation. As has been shown in many
investigations, they are, in the undisturbed development, under correlative inhibition caused by the presence of an actively growing
meristematic centre. Their further development after reactivation
usually follows the course of normal development. Only a few cases in
lower plants have been studied in this respect. Nevertheless, these
investigations have contributed to the discussion about the nature of
correlative inhibition of latent primordia by the actively growing apical
centre, the phenomenon of the so-called apical dominance.
In the moss Funaria hygrometrica the phenomenon of apical dominance has been studied by Sironval (1952). In plants with an intact apex
some lateral branches occasionally occurred but were always restricted
to the base of the gametophore. On the other hand, after decapitation of
the apex of gametophores, lateral buds grew out, mainly in the upper
part of the gametophore and to a lesser extent in its middle and basal
regions. Lateral buds also grew out from isolated segments of the stem
(cf. Ainsworth, 1956). Stem segments without a bud regenerated protonemà. The possible influence of the apex in the correlative inhibition of
lateral buds was examined also by MacQuarrie and von Maltzahn (1959)
in the moss Splachnum ampullaceum by comparing lateral bud behaviour
in decapitated and intact plants. The results were evaluated by calculating the percentage of branches per axil present in the plants. While
in intact plants the percentage of growing lateral branches varied between 0 and 29% (depending on the different experiments), in decapitated plants 57-97% buds were reactivated. Removal of the apical
region, therefore, resulted in the removal of influences which inhibited
the activity of lateral buds. It was also observed that in later stages of
development of intact gametophores a considerable amount of lateral