112
LUISE STANGE
losses opens new possibilities for the experimental analysis of these
developmental activities. Since the start of experimental work in plant
morphogenesis in the last century, the induction of regeneration had
become one of the favoured methods in the investigation of developmental processes. The investigation of developmental processes in
plants by induction of regeneration is the subject of this chapter. We
shall restrict ourselves to three developmental phenomena, the analysis
of which has been particularly promoted by the method of induction of
regeneration.
In plants usually two different types of regeneration are distinguished.
One way in which regeneration is brought about is by the activation of
dormant buds or primordia. The critical process here is the reactivation
of a preformed but quiescent meristematic centre (Section II). In the
second type of regeneration, mature cells may become embryonic again
and produce lost parts or whole new plants. The changes occurring
during this process in the mature cells are usually referred to as 'dedifferentiation'. Since these changes are not only an involution of
structures and properties evolved in connexion with special functions,
but even more important, a recovery of the embryonic properties, we
prefer to refer to these processes as 'embryonization' (Section III).
Especially in this type of regeneration, the conditions under which the
regenerate develops can be very different from the conditions in normal
development. Therefore, the differentiation of the regenerate may give
some information about the developmental potentialities of the regenerating cell and about influences of adjacent cells on differentiation
(Section IV).
This chapter has been restricted to lower plants for the following
reasons. Generally the more simple and undififerentiated a plant is, the
higher is its regenerative capacity, and the more highly developed and
differentiated it is, the less completely will it restore missing parts.
Thus, plants of the lower groups in the phylogenetic scale usually show
a high regenerative capacity. There is another difference between lower
and higher plants which is important in this connexion. In most of the
lower plants a single cell can have the ability to develop readily into a
whole plant, and they often do so as a means of reproduction and propagation. However, in the normal development of spermatophytes,
isolated single cells do not occur. This independence of single cells in
lower plants can be assumed to be related to their lower level of organization. Furthermore, the lower plants offer the advantage, not realized
in higher plants, that the gametophyte and the sporophyte can be
obtained and grown separately. Regeneration of isolated parts of both
generations takes place readily. The occurrence of apospory and
apogamy and the possibility of their experimental induction allows
LUISE STANGE
losses opens new possibilities for the experimental analysis of these
developmental activities. Since the start of experimental work in plant
morphogenesis in the last century, the induction of regeneration had
become one of the favoured methods in the investigation of developmental processes. The investigation of developmental processes in
plants by induction of regeneration is the subject of this chapter. We
shall restrict ourselves to three developmental phenomena, the analysis
of which has been particularly promoted by the method of induction of
regeneration.
In plants usually two different types of regeneration are distinguished.
One way in which regeneration is brought about is by the activation of
dormant buds or primordia. The critical process here is the reactivation
of a preformed but quiescent meristematic centre (Section II). In the
second type of regeneration, mature cells may become embryonic again
and produce lost parts or whole new plants. The changes occurring
during this process in the mature cells are usually referred to as 'dedifferentiation'. Since these changes are not only an involution of
structures and properties evolved in connexion with special functions,
but even more important, a recovery of the embryonic properties, we
prefer to refer to these processes as 'embryonization' (Section III).
Especially in this type of regeneration, the conditions under which the
regenerate develops can be very different from the conditions in normal
development. Therefore, the differentiation of the regenerate may give
some information about the developmental potentialities of the regenerating cell and about influences of adjacent cells on differentiation
(Section IV).
This chapter has been restricted to lower plants for the following
reasons. Generally the more simple and undififerentiated a plant is, the
higher is its regenerative capacity, and the more highly developed and
differentiated it is, the less completely will it restore missing parts.
Thus, plants of the lower groups in the phylogenetic scale usually show
a high regenerative capacity. There is another difference between lower
and higher plants which is important in this connexion. In most of the
lower plants a single cell can have the ability to develop readily into a
whole plant, and they often do so as a means of reproduction and propagation. However, in the normal development of spermatophytes,
isolated single cells do not occur. This independence of single cells in
lower plants can be assumed to be related to their lower level of organization. Furthermore, the lower plants offer the advantage, not realized
in higher plants, that the gametophyte and the sporophyte can be
obtained and grown separately. Regeneration of isolated parts of both
generations takes place readily. The occurrence of apospory and
apogamy and the possibility of their experimental induction allows