116
LUISE STANGE
plants immediately following decapitation. Lateral bud reactivation
was examined 4 days after the beginning of the treatment. The results
are given in Table I. Kinetin is seen to have a strong antagonistic effect
on the action of IAA in so far as it promotes lateral bud reactivation in
the presence of IAA. These results indicate that reactivation of lateral
buds in the moss gametophore also may be controlled by an interaction
between auxin and kinetin. A comparison of these results with the effect
of auxin and kinetin on regeneration through embryonization in
Splachnum will be given in Section III, C.
In his investigations on apical dominance in Marsilea, Allsopp (1956)
pointed out that this plant is specially suitable to test the hypothesis of
direct inhibition of lateral buds by auxin. Plants or excised nodes of
Marsilea are cultivated aseptically in liquid medium to which auxin in
an appropriate concentration range can be added. Since aquatic plants
absorb readily over their whole surface, it is assumed that there is no
restriction in the access of the added auxin to the cell. According to
the hypothesis of direct inhibition, it must be expected that concentrations of auxin which promote the elongation of the main shoot should
also prevent the outgrowth of lateral buds. IAA and indoleacetonitrile
(IAN) in concentrations of 10
-5
, 10
-6
and 10~
7
g/ml were used, a range
in which these auxins exert their maximum effect on cell elongation of
Avena coleoptiles (Bentley and Housley, 1952). In the two lower concentrations of IAA and in all concentrations of IAN slight to strong
increase of elongation of petioles and internodes was observed in intact
plants of Marsilea (cf. also Allsopp, 1954), while in the highest concentration of IAA toxic effects were evident. As to the behaviour of
lateral buds after decapitation, however, no differences were found between plants in medium without or with auxin in all concentrations
applied; all decapitated plants produced lateral shoots from the buds
nearest the apical cut surface. Likewise in excised nodes, lateral buds
developed into lateral branches in all concentrations of IAA and IAN.
From these results Allsopp concludes 'that direct inhibition by auxin
plays little or no part in the correlative inhibition of lateral buds'.
However, no other suggestion is offered from these experiments for an
explanation of the apical. dominance in the intact plant. We shall
return to the question of the role of auxin in correlative inhibition once
again in discussing the influence of auxin in differentiation (Section
III.C).
III. Embryonization of Mature Cells
The essential feature of the developmental process is the origin of
differences between the various parts of an individual. This process of
morphological and physiological differentiation is fin expression of a
LUISE STANGE
plants immediately following decapitation. Lateral bud reactivation
was examined 4 days after the beginning of the treatment. The results
are given in Table I. Kinetin is seen to have a strong antagonistic effect
on the action of IAA in so far as it promotes lateral bud reactivation in
the presence of IAA. These results indicate that reactivation of lateral
buds in the moss gametophore also may be controlled by an interaction
between auxin and kinetin. A comparison of these results with the effect
of auxin and kinetin on regeneration through embryonization in
Splachnum will be given in Section III, C.
In his investigations on apical dominance in Marsilea, Allsopp (1956)
pointed out that this plant is specially suitable to test the hypothesis of
direct inhibition of lateral buds by auxin. Plants or excised nodes of
Marsilea are cultivated aseptically in liquid medium to which auxin in
an appropriate concentration range can be added. Since aquatic plants
absorb readily over their whole surface, it is assumed that there is no
restriction in the access of the added auxin to the cell. According to
the hypothesis of direct inhibition, it must be expected that concentrations of auxin which promote the elongation of the main shoot should
also prevent the outgrowth of lateral buds. IAA and indoleacetonitrile
(IAN) in concentrations of 10
-5
, 10
-6
and 10~
7
g/ml were used, a range
in which these auxins exert their maximum effect on cell elongation of
Avena coleoptiles (Bentley and Housley, 1952). In the two lower concentrations of IAA and in all concentrations of IAN slight to strong
increase of elongation of petioles and internodes was observed in intact
plants of Marsilea (cf. also Allsopp, 1954), while in the highest concentration of IAA toxic effects were evident. As to the behaviour of
lateral buds after decapitation, however, no differences were found between plants in medium without or with auxin in all concentrations
applied; all decapitated plants produced lateral shoots from the buds
nearest the apical cut surface. Likewise in excised nodes, lateral buds
developed into lateral branches in all concentrations of IAA and IAN.
From these results Allsopp concludes 'that direct inhibition by auxin
plays little or no part in the correlative inhibition of lateral buds'.
However, no other suggestion is offered from these experiments for an
explanation of the apical. dominance in the intact plant. We shall
return to the question of the role of auxin in correlative inhibition once
again in discussing the influence of auxin in differentiation (Section
III.C).
III. Embryonization of Mature Cells
The essential feature of the developmental process is the origin of
differences between the various parts of an individual. This process of
morphological and physiological differentiation is fin expression of a