216
J. HESLOP-HARRISON
type. In one experiment, eight combinations of nitrogen, phosphorus
and potassium fertilizer treatments were given to a parental generation,
and effects on weight of progeny were observed for four generations
under uniform soil conditions. I n the second generation, the descendants
of plants receiving N K but not P weighed only one-third of those receiving PK. The “genotrophs” or conditioned form6 differed in morphological features other than gross production, and revealed various
physiological peculiarities. Durrant has referred to them as being
adapted to different environments, and it is evident from his data that
their performance does not always bear the same relationship to the
“normal” under diverse conditions of cultivation in the open and in
greenhouses. It is not apparent, however, that the effect of conditioning
in flax is necessarily to produce a genotroph better adapted to the soil
environment inducing the change.
The possibility that environmental conditioning in flax might
depend upon the behaviour of cytoplasmic determinants was considered by Durrant (1958), but later abandoned (1962). The suggestion
was that under the inducing conditions the relative multiplication rate of
nuclear genes and plasmagenes might be affected, so establishing a new
nuclear-cytoplasmic relationship. Should this new relationship constitute a stable equilibrium, the condition might be propagated through
successive generations. Essentially the same suggestion had previously
been made by Crosby (1956) as a theoretical basis for the inheritance of
acquired adaptations. A model system is described by Crosby in which a
plant is presumed to be adapted to a mild environment with a low concentration of a plasmagene favouring resistance to low temperatures.
Under cooler conditions, growth rate and so cell division rate is reduced.
If it be assumed that the rate of reproduction of the plasmagenes concerned with cold resistance is not reduced proportionately, then their
concentration will increase in the cell, so progressively enhancing cold
tolerance. If the conditioned state is transmitted through the reproductive cells, then progeny will be better equipped to survive in the cooler
environment.
Crosby emphasizes that acquired adaptation of this kind is most
likely to be found in generalized characteristics like growth and vigour;
it is in these features that Durrant’s genotrophs differ most from their
parental strains. The response as envisaged by Crosby and Durrant may
be looked upon as a sort of physiological adjustment of phenotype to
environment akin to that involved in the conditioning of individuals
k i n g growth, but having a transmitted element providing for the
partial pre-adaptation of progeny. Certainly there is no need to discount
this possibility on any physiological grounds. It is well known that
induced states such as those arising from vernalization and photo-
J. HESLOP-HARRISON
type. In one experiment, eight combinations of nitrogen, phosphorus
and potassium fertilizer treatments were given to a parental generation,
and effects on weight of progeny were observed for four generations
under uniform soil conditions. I n the second generation, the descendants
of plants receiving N K but not P weighed only one-third of those receiving PK. The “genotrophs” or conditioned form6 differed in morphological features other than gross production, and revealed various
physiological peculiarities. Durrant has referred to them as being
adapted to different environments, and it is evident from his data that
their performance does not always bear the same relationship to the
“normal” under diverse conditions of cultivation in the open and in
greenhouses. It is not apparent, however, that the effect of conditioning
in flax is necessarily to produce a genotroph better adapted to the soil
environment inducing the change.
The possibility that environmental conditioning in flax might
depend upon the behaviour of cytoplasmic determinants was considered by Durrant (1958), but later abandoned (1962). The suggestion
was that under the inducing conditions the relative multiplication rate of
nuclear genes and plasmagenes might be affected, so establishing a new
nuclear-cytoplasmic relationship. Should this new relationship constitute a stable equilibrium, the condition might be propagated through
successive generations. Essentially the same suggestion had previously
been made by Crosby (1956) as a theoretical basis for the inheritance of
acquired adaptations. A model system is described by Crosby in which a
plant is presumed to be adapted to a mild environment with a low concentration of a plasmagene favouring resistance to low temperatures.
Under cooler conditions, growth rate and so cell division rate is reduced.
If it be assumed that the rate of reproduction of the plasmagenes concerned with cold resistance is not reduced proportionately, then their
concentration will increase in the cell, so progressively enhancing cold
tolerance. If the conditioned state is transmitted through the reproductive cells, then progeny will be better equipped to survive in the cooler
environment.
Crosby emphasizes that acquired adaptation of this kind is most
likely to be found in generalized characteristics like growth and vigour;
it is in these features that Durrant’s genotrophs differ most from their
parental strains. The response as envisaged by Crosby and Durrant may
be looked upon as a sort of physiological adjustment of phenotype to
environment akin to that involved in the conditioning of individuals
k i n g growth, but having a transmitted element providing for the
partial pre-adaptation of progeny. Certainly there is no need to discount
this possibility on any physiological grounds. It is well known that
induced states such as those arising from vernalization and photo-