56
SIRKKA KUPILA-AHVENNIEMI AND EEVA THERMAN
along these lines have been reviewed by Bloch (1941, 1952). The investigations of, for example, Clowes (1953, 1954) and Ball (1956) on
the root tip and by Ball (1952, 1955) and Cutter (1957; see also Cutter,
1965) on the shoot tip have confirmed the surprising ability of the
meristematic cells for repeated cell division and tissue organization. In
the more differentiated organs the reaction is restricted. In the stem,
the stele tissues and the cambium are usually the most reactive parts.
The reaction of the cells in the other tissue systems differs from species
to species. Third, the degree and type of cell differentiation often determines how easily and rapidly the cells react to the wound stimulus. As a
rule, the highly differentiated cells, such as tracheids, sieve elements,
companion cells, and fibers are not able to dedifferentiate and divide.
That wounding often retards the elongation of the affected plant organ
has been shown repeatedly (see Biinning, 1959; Kupila and Stern, 1961;
Kupila-Ahvenniemi, 1966). In a few days, however, this effect may be
overcome.
Certain anatomical features appear to be more or less common to the
wound-healing processes of the higher plants. As a rule, the first clearly
visible indication of wound reaction is the appearance of cell divisions.
The new cell walls are recognizable by their relative thinness and their
direction, which most commonly is parallel to the wound surface; other
directions may occur at later stages of wound healing. Another feature
characteristic of these early cell divisions is the position of the new walls
in adjacent cells. Often they arise side by side so that corners of four cells
are formed (Sinnott and Bloch, 1941). These two phenomena result in
the formation of regular cell rows running toward the wound edge.
Fellenberg and Bopp (1966) have recently studied the formation of
cell rows after wounding in Kalanchoe daigremontiana.
All the wounds
were deep enough to reach the pith. The observations were made during
16 days. An increase in the number of cells was taken as a proof of continuous cell division. The cells showed a continuous anticlinal growth,
but, because of periclinal divisions, additional cell rows were formed,
and these diminished the mean periclinal diameter of the cells.
The wound reaction of the stem of K. daigremontiana
was studied by
Bopp and Leppla (1964) in connection with crown gall induction. The
authors observed the first cell divisions to take place in the cortex, the
epidermis, and the hypodermis. Oriented cell divisions were first seen
4 days after wounding, and after 3 to 5 more days they had produced
cell rows running to the wound edge. The division stimulus seemed to
spread into the cortex forcing also the cells at some distance from the
SIRKKA KUPILA-AHVENNIEMI AND EEVA THERMAN
along these lines have been reviewed by Bloch (1941, 1952). The investigations of, for example, Clowes (1953, 1954) and Ball (1956) on
the root tip and by Ball (1952, 1955) and Cutter (1957; see also Cutter,
1965) on the shoot tip have confirmed the surprising ability of the
meristematic cells for repeated cell division and tissue organization. In
the more differentiated organs the reaction is restricted. In the stem,
the stele tissues and the cambium are usually the most reactive parts.
The reaction of the cells in the other tissue systems differs from species
to species. Third, the degree and type of cell differentiation often determines how easily and rapidly the cells react to the wound stimulus. As a
rule, the highly differentiated cells, such as tracheids, sieve elements,
companion cells, and fibers are not able to dedifferentiate and divide.
That wounding often retards the elongation of the affected plant organ
has been shown repeatedly (see Biinning, 1959; Kupila and Stern, 1961;
Kupila-Ahvenniemi, 1966). In a few days, however, this effect may be
overcome.
Certain anatomical features appear to be more or less common to the
wound-healing processes of the higher plants. As a rule, the first clearly
visible indication of wound reaction is the appearance of cell divisions.
The new cell walls are recognizable by their relative thinness and their
direction, which most commonly is parallel to the wound surface; other
directions may occur at later stages of wound healing. Another feature
characteristic of these early cell divisions is the position of the new walls
in adjacent cells. Often they arise side by side so that corners of four cells
are formed (Sinnott and Bloch, 1941). These two phenomena result in
the formation of regular cell rows running toward the wound edge.
Fellenberg and Bopp (1966) have recently studied the formation of
cell rows after wounding in Kalanchoe daigremontiana.
All the wounds
were deep enough to reach the pith. The observations were made during
16 days. An increase in the number of cells was taken as a proof of continuous cell division. The cells showed a continuous anticlinal growth,
but, because of periclinal divisions, additional cell rows were formed,
and these diminished the mean periclinal diameter of the cells.
The wound reaction of the stem of K. daigremontiana
was studied by
Bopp and Leppla (1964) in connection with crown gall induction. The
authors observed the first cell divisions to take place in the cortex, the
epidermis, and the hypodermis. Oriented cell divisions were first seen
4 days after wounding, and after 3 to 5 more days they had produced
cell rows running to the wound edge. The division stimulus seemed to
spread into the cortex forcing also the cells at some distance from the