HETEROBLASTIC DEVELOPMENT IN VASCULAR PLANTS
A. ALLSOPP
Department of Cryptogamic Botany, The University, Manchester, England
I. Introduction
127
II. Morphological Characteristics
128
A. Changes in Leaf Morphology
128
B. Changes in Stem Characteristics
132
III. Interpretations and Experimental Studies
135
A. Phylogeny and Recapitulation
135
B. The Role of Primary Enlargement
137
C. The Role of Nutrition
138
D. The Ontogeny of Leaf Primordia
151
E. The Effects of Environment
153
F. The Role of Physiological Aging
156
G. Genetical Aspects
164
IV. Conclusions
166
References
167
I. Introduction
The normal course of plant ontogeny, from seed or spore to the formation of reproductive organs, is usually characterized by the development
of more or less pronounced morphological differences between the successively produced vegetative parts or organs. Following Goebel (1898),
such morphological changes are frequently referred to as heteroblastic
development in contrast to homoblastic development, in which no marked
morphological changes occur. As recognized by Goebel himself, there is
no sharp distinction between these two types of development, and in one
sense virtually all plants are heteroblastic, since there are always obvious
differences between the vegetative and reproductive organs. The changes
in the vegetative parts are an extensive subject in themselves, however,
and in conformity with the accepted connotation of heteroblastic development, this article is restricted in the main to a consideration of such
changes.
During recent years, there has been a considerable expansion of interest
in heteroblastic development, an interest which is understandable when it
is considered that the observed morphological changes reflect the progress
of the plant towards maturity and the associated capacity for the pro127
A. ALLSOPP
Department of Cryptogamic Botany, The University, Manchester, England
I. Introduction
127
II. Morphological Characteristics
128
A. Changes in Leaf Morphology
128
B. Changes in Stem Characteristics
132
III. Interpretations and Experimental Studies
135
A. Phylogeny and Recapitulation
135
B. The Role of Primary Enlargement
137
C. The Role of Nutrition
138
D. The Ontogeny of Leaf Primordia
151
E. The Effects of Environment
153
F. The Role of Physiological Aging
156
G. Genetical Aspects
164
IV. Conclusions
166
References
167
I. Introduction
The normal course of plant ontogeny, from seed or spore to the formation of reproductive organs, is usually characterized by the development
of more or less pronounced morphological differences between the successively produced vegetative parts or organs. Following Goebel (1898),
such morphological changes are frequently referred to as heteroblastic
development in contrast to homoblastic development, in which no marked
morphological changes occur. As recognized by Goebel himself, there is
no sharp distinction between these two types of development, and in one
sense virtually all plants are heteroblastic, since there are always obvious
differences between the vegetative and reproductive organs. The changes
in the vegetative parts are an extensive subject in themselves, however,
and in conformity with the accepted connotation of heteroblastic development, this article is restricted in the main to a consideration of such
changes.
During recent years, there has been a considerable expansion of interest
in heteroblastic development, an interest which is understandable when it
is considered that the observed morphological changes reflect the progress
of the plant towards maturity and the associated capacity for the pro127