40
JOHN G. TORREY
outlined, requiring only detailed analytical study to unravel specific
pathways in each case.
In multicellular organisms, at a higher level of organization, cellular
populations arise which are arranged in particular structural configurations forming organized tissue systems and organs. Here again is reflected the genie information, but at the multicellular and organismic
level. Genetic control of organ formation derives from gene control both
of cell function and of the correlated functioning of cell populations.
In multicellular systems, such as the higher green plant, cells interact
in complex fashion. Closely associated cells interact by the exchange of
metabolites, the movement of substrates from source to sink, or the release of specific products of specialized cell synthesis. Despite rigid
cellulosic walls, many plant cells are intimately associated by intercellular connections with cytoplasmic continuity. From such cellular interactions result coordinated cellular arrays or tissue systems showing
precise and characteristic patterns of cellular differentiation.
At the highest level of complexity, cells and tissue systems are coordinated during their formation into recognizable morphological arrangements as shoots, leaves, roots, flowers, and fruits. These are the structures
we usually recognize as the characteristic phenotype of the organism.
Such organs may perform specialized functions, act as centers of specific
syntheses, or serve as storage depots for the organism. Yet organization
at this level is ultimately interprétable in terms of cellular activities. It is
the problem of modern biology to work out the mechanisms whereby
cellular activities under more or less direct genetic control are coordinated and correlated so as to result in the development of multicellular
structures of precise organization.
Cell, tissue, and organ initiation in plants appear to form categories
of morphological expression, each under genetic control ; all act together,
each at its own level of complexity, to form a coordinated whole organism. In the intact plant, one is faced with such integrated activity as to
make analysis of the interacting internal forces difficult. By experimentally isolating organs, or tissues, or even individual cells and studying
their activities in isolation, it becomes possible to separate spatially the
interacting systems and thereby to gain some insight into these interactions. Thus organ, tissue, and cell cultures have been of great service
in helping to reveal the interdependencies that exist between different
organs of the plant and the mechanisms whereby cells and tissues and
organs interact during development.
In tissue and cell cultures, some of the physiological control mechanisms for organized development are clearly wiped out by the isolation
associated with in vitro culture techniques. A rapidly proliferating mass
JOHN G. TORREY
outlined, requiring only detailed analytical study to unravel specific
pathways in each case.
In multicellular organisms, at a higher level of organization, cellular
populations arise which are arranged in particular structural configurations forming organized tissue systems and organs. Here again is reflected the genie information, but at the multicellular and organismic
level. Genetic control of organ formation derives from gene control both
of cell function and of the correlated functioning of cell populations.
In multicellular systems, such as the higher green plant, cells interact
in complex fashion. Closely associated cells interact by the exchange of
metabolites, the movement of substrates from source to sink, or the release of specific products of specialized cell synthesis. Despite rigid
cellulosic walls, many plant cells are intimately associated by intercellular connections with cytoplasmic continuity. From such cellular interactions result coordinated cellular arrays or tissue systems showing
precise and characteristic patterns of cellular differentiation.
At the highest level of complexity, cells and tissue systems are coordinated during their formation into recognizable morphological arrangements as shoots, leaves, roots, flowers, and fruits. These are the structures
we usually recognize as the characteristic phenotype of the organism.
Such organs may perform specialized functions, act as centers of specific
syntheses, or serve as storage depots for the organism. Yet organization
at this level is ultimately interprétable in terms of cellular activities. It is
the problem of modern biology to work out the mechanisms whereby
cellular activities under more or less direct genetic control are coordinated and correlated so as to result in the development of multicellular
structures of precise organization.
Cell, tissue, and organ initiation in plants appear to form categories
of morphological expression, each under genetic control ; all act together,
each at its own level of complexity, to form a coordinated whole organism. In the intact plant, one is faced with such integrated activity as to
make analysis of the interacting internal forces difficult. By experimentally isolating organs, or tissues, or even individual cells and studying
their activities in isolation, it becomes possible to separate spatially the
interacting systems and thereby to gain some insight into these interactions. Thus organ, tissue, and cell cultures have been of great service
in helping to reveal the interdependencies that exist between different
organs of the plant and the mechanisms whereby cells and tissues and
organs interact during development.
In tissue and cell cultures, some of the physiological control mechanisms for organized development are clearly wiped out by the isolation
associated with in vitro culture techniques. A rapidly proliferating mass