HETEROBLASTIC DEVELOPMENT IN PLANTS
167
was shown that changes in the carbohydrate balance produce drastic
morphological changes, and it seems likely that such changes are important in normal heteroblastic development, although other factors are
not excluded. It was also shown that changes in carbohydrate balance
can act directly on all meristematic tissues including those of the leaf.
The morphological characteristics of this second type of heteroblastic
development, unlike those of the first type, are thus relatively independent of the ontogenetic level attained by the shoot apical meristem.
There is also no conclusive evidence that physiological aging is determined by any intrinsic aging of the mature tissues of the plant. The
changes in physiological condition might result as a more or less automatic consequence of the characteristics of plant growth, in which there
is evidence that an expansion of the photosynthetic surface is paralleled
by an increasing difficulty in the supply of nitrogen and other elements
to the living and particularly to the meristematic parts of the plant.
There is no necessity to postulate that specific youth hormones are
involved.
The morphological changes associated with physiological aging are so
varied and specific that it is unlikely that they are the direct result of
the changes in the balance of metabolites. A whole set of new morphological potentialities is often revealed. A plausible explanation of these
changes invokes a regulatory effect of the intracellular environment on
gene activity. But it is not even certain that changes in gene activity
are necessary. A more immediate effect of metabolites on enzyme synthesis and activity might be involved. Only more detailed studies of
cellular metabolism can supply the answers.
Acknowledgments
I am grateful to the authors and publishers for permission to reproduce Figs. 1
and 2, and to Mr. Geoffrey Grange and Mr. Colin Dean for preparing these figures
for publication. I am also indebted to the Clarendon Press, Oxford, England, for
permitting the reproduction of Figs. 3-8.
References
Allsopp, A. (1951). Nature 168, 301.
Allsopp, A. (1952). Ann. Botany {London) 16, 165.
Allsopp, A. (1953a). Ann. Botany {London) 17, 37.
Allsopp, A. (1953b). Ann. Botany {London) 17, 447.
Allsopp, A. (1954a). Ann. Botany {London) 18, 449.
Allsopp, A. (1954b). / . Exptl. Botany 5, 16.
Allsopp, A. (1954c). Nature 173, 1032.
Allsopp, A. (1955). Ann. Botany {London) 19, 247.
Allsopp, A. (1956). J. Exptl. Botany 7, 14.
Allsopp, A. (1962). Phytomorphology 12, 1.
Allsopp, A. (1963). / . Linnean Soc. {Botany) 58, 417.
167
was shown that changes in the carbohydrate balance produce drastic
morphological changes, and it seems likely that such changes are important in normal heteroblastic development, although other factors are
not excluded. It was also shown that changes in carbohydrate balance
can act directly on all meristematic tissues including those of the leaf.
The morphological characteristics of this second type of heteroblastic
development, unlike those of the first type, are thus relatively independent of the ontogenetic level attained by the shoot apical meristem.
There is also no conclusive evidence that physiological aging is determined by any intrinsic aging of the mature tissues of the plant. The
changes in physiological condition might result as a more or less automatic consequence of the characteristics of plant growth, in which there
is evidence that an expansion of the photosynthetic surface is paralleled
by an increasing difficulty in the supply of nitrogen and other elements
to the living and particularly to the meristematic parts of the plant.
There is no necessity to postulate that specific youth hormones are
involved.
The morphological changes associated with physiological aging are so
varied and specific that it is unlikely that they are the direct result of
the changes in the balance of metabolites. A whole set of new morphological potentialities is often revealed. A plausible explanation of these
changes invokes a regulatory effect of the intracellular environment on
gene activity. But it is not even certain that changes in gene activity
are necessary. A more immediate effect of metabolites on enzyme synthesis and activity might be involved. Only more detailed studies of
cellular metabolism can supply the answers.
Acknowledgments
I am grateful to the authors and publishers for permission to reproduce Figs. 1
and 2, and to Mr. Geoffrey Grange and Mr. Colin Dean for preparing these figures
for publication. I am also indebted to the Clarendon Press, Oxford, England, for
permitting the reproduction of Figs. 3-8.
References
Allsopp, A. (1951). Nature 168, 301.
Allsopp, A. (1952). Ann. Botany {London) 16, 165.
Allsopp, A. (1953a). Ann. Botany {London) 17, 37.
Allsopp, A. (1953b). Ann. Botany {London) 17, 447.
Allsopp, A. (1954a). Ann. Botany {London) 18, 449.
Allsopp, A. (1954b). / . Exptl. Botany 5, 16.
Allsopp, A. (1954c). Nature 173, 1032.
Allsopp, A. (1955). Ann. Botany {London) 19, 247.
Allsopp, A. (1956). J. Exptl. Botany 7, 14.
Allsopp, A. (1962). Phytomorphology 12, 1.
Allsopp, A. (1963). / . Linnean Soc. {Botany) 58, 417.