ORGANIZED DEVELOPMENT IN PLANTS
83
question of the determination of leaves and the conversion of leaf primordia into buds. The experimental work on this subject has been reviewed recently by Steeves (1962) and by Allsopp (1964). Here again
the angiosperms appear to differ from ferns. Isolated leaf primordia of
Helianthus
annuus or Nicotiana
in culture produced only leaves, not
whole plants, whereas very small isolated leaf primordia of the ferns
Dryopteris or Osmunda in many cases formed shoots and finally whole
plants. The basic differences between angiosperms and other major
groups of vascular plants in this respect remain to be elucidated. However, it does seem clear that, in the angiosperms, partially or wellorganized structures may be limited in expressing inherent but masked
capacities to organize if they do not pass or cannot be forced to pass
through a developmental course in which their inherent correlative (hormonal?) mechanisms are suppressed or eliminated.
Recently, apical meristem culture has taken on a novel interest with
the recognition of its potential application to commercial propagation of
important horticultural species. Morel (1964) found in certain orchids,
e.g., Cymbidiam
and Cattleya, that isolated apical meristems with one
or two leaf primordia attached when grown in a nutrient medium formed
an enlarged protocorm which in a few weeks could be cut into quarters,
each subcultured piece, in turn, forming a new protocorm which could
be subsequently sectored. From each protocorm would grow a whole
plant if at any stage it was not subdivided for further subcultures. Since
the apical meristem cultures can be started from adult plants which have
flowered and demonstrated their value, it is clear that here is a technique
for vegetative propagation of a particular genetic line without loss of the
desirable genetic characters (a loss which is almost certain to occur in
sexually reproduced orchid plants). It is of interest that here the inherent capacity to organize a new protocorm, and, indeed, a whole plant,
is made use of in the propagation procedure. These plants are frequently
very difficult to propagate by other asexual methods, and, thus, the
method has potential value in the propagation of such species.
Wimber (1963) reported that such protocorms also developed in liquid
medium with continuous agitation. Here, the similarity in technique and
result to that of Steward et al. (1964), Halperin and Wetherell (1964),
and others on embryo formation in callus tissue becomes immediately
obvious. One cannot help but extrapolate this and related techniques to
the propagation of many other plants of importance to man which are
propagated only by asexual methods (for example, the navel orange) or
are difficult to propagate by usual vegetative reproduction methods. The
whole field of tissue culture propagation would seem to offer a remarkable opportunity for plant engineering.
83
question of the determination of leaves and the conversion of leaf primordia into buds. The experimental work on this subject has been reviewed recently by Steeves (1962) and by Allsopp (1964). Here again
the angiosperms appear to differ from ferns. Isolated leaf primordia of
Helianthus
annuus or Nicotiana
in culture produced only leaves, not
whole plants, whereas very small isolated leaf primordia of the ferns
Dryopteris or Osmunda in many cases formed shoots and finally whole
plants. The basic differences between angiosperms and other major
groups of vascular plants in this respect remain to be elucidated. However, it does seem clear that, in the angiosperms, partially or wellorganized structures may be limited in expressing inherent but masked
capacities to organize if they do not pass or cannot be forced to pass
through a developmental course in which their inherent correlative (hormonal?) mechanisms are suppressed or eliminated.
Recently, apical meristem culture has taken on a novel interest with
the recognition of its potential application to commercial propagation of
important horticultural species. Morel (1964) found in certain orchids,
e.g., Cymbidiam
and Cattleya, that isolated apical meristems with one
or two leaf primordia attached when grown in a nutrient medium formed
an enlarged protocorm which in a few weeks could be cut into quarters,
each subcultured piece, in turn, forming a new protocorm which could
be subsequently sectored. From each protocorm would grow a whole
plant if at any stage it was not subdivided for further subcultures. Since
the apical meristem cultures can be started from adult plants which have
flowered and demonstrated their value, it is clear that here is a technique
for vegetative propagation of a particular genetic line without loss of the
desirable genetic characters (a loss which is almost certain to occur in
sexually reproduced orchid plants). It is of interest that here the inherent capacity to organize a new protocorm, and, indeed, a whole plant,
is made use of in the propagation procedure. These plants are frequently
very difficult to propagate by other asexual methods, and, thus, the
method has potential value in the propagation of such species.
Wimber (1963) reported that such protocorms also developed in liquid
medium with continuous agitation. Here, the similarity in technique and
result to that of Steward et al. (1964), Halperin and Wetherell (1964),
and others on embryo formation in callus tissue becomes immediately
obvious. One cannot help but extrapolate this and related techniques to
the propagation of many other plants of importance to man which are
propagated only by asexual methods (for example, the navel orange) or
are difficult to propagate by usual vegetative reproduction methods. The
whole field of tissue culture propagation would seem to offer a remarkable opportunity for plant engineering.