60
SIRKKA KUPILA-AHVENNIEMI AND EEVA THERMAN
older tumor have not been properly studied. In some cases the xylem
and the phloem have united to form relatively normal-looking vascular
bundles.
The reason for calling this type of gall a teratoma lies in its anatomical
structure (Kupila, 1958). As has been mentioned earlier, the studies of
Braun (1953) have shown that a moderately virulent strain of crown
gall bacteria, when inoculated to a lower cut surface of the tobacco
stem, induces tumors bearing distorted shoots and buds. The galls
growing on the base of the cut shoot as well as the galls formed on
an uncut stem have a more or less smooth surface. The appearance
of the growth centers and the strands of the connecting tissue indicates
that the tendency to form organs still exists in the gall tissue but that
it is overcome by the rapidity of the cell divisions and the lack of any
polarity.
The development of the crown gall in the stem of the sunflower differs
considerably from the development of the teratoma-type galls. Braun
(1953) called the galls with more or less smooth surface the "unorganized" type regardless of the inner structure. The sunflower gall has been
named unorganized on the basis of its anatomical development and
structure (Kupila, 1958). The developmental pattern of the gall is
the following: After inoculation the reaction of the cells close to the
wound is rapid and vigorous. In a few days numerous cell divisions
in parallel planes cause the formation of long cell rows. These rows are
oriented toward the wound edge and appear in the pith and the cortex
as well as in the stele. Soon, however, the cells in the pith and the
cortex region enlarge and round up so that they resemble the original
pith and cortex cells. Cell divisions continue, especially in the pith,
increasing the tissue in the original wound gap. Simultaneously the cells
in the cambial area form a new tissue which has been called the "tumor
cambium." This layer of narrow, rapidly dividing cells lies at a certain
distance from the wound edge. It originates in the cambial area but the
stimulus to orderly cell divisions obviously diffuses to the neighboring
cells, especially toward the pith, and after a while a meristematic layer
develops around the wound. The increasing tissue in the pith pushes this
layer outward so that the normal and the tumorous meristematic areas
come to form a cylinder.
The cell divisions in the tumor cambium are not as regular and controlled as in the normal cambium. The tissue proliferation is so rapid
that the layer not only thickens abnormally but also becomes wavy. It
forms protuberances that push toward the gall surface crushing other
SIRKKA KUPILA-AHVENNIEMI AND EEVA THERMAN
older tumor have not been properly studied. In some cases the xylem
and the phloem have united to form relatively normal-looking vascular
bundles.
The reason for calling this type of gall a teratoma lies in its anatomical
structure (Kupila, 1958). As has been mentioned earlier, the studies of
Braun (1953) have shown that a moderately virulent strain of crown
gall bacteria, when inoculated to a lower cut surface of the tobacco
stem, induces tumors bearing distorted shoots and buds. The galls
growing on the base of the cut shoot as well as the galls formed on
an uncut stem have a more or less smooth surface. The appearance
of the growth centers and the strands of the connecting tissue indicates
that the tendency to form organs still exists in the gall tissue but that
it is overcome by the rapidity of the cell divisions and the lack of any
polarity.
The development of the crown gall in the stem of the sunflower differs
considerably from the development of the teratoma-type galls. Braun
(1953) called the galls with more or less smooth surface the "unorganized" type regardless of the inner structure. The sunflower gall has been
named unorganized on the basis of its anatomical development and
structure (Kupila, 1958). The developmental pattern of the gall is
the following: After inoculation the reaction of the cells close to the
wound is rapid and vigorous. In a few days numerous cell divisions
in parallel planes cause the formation of long cell rows. These rows are
oriented toward the wound edge and appear in the pith and the cortex
as well as in the stele. Soon, however, the cells in the pith and the
cortex region enlarge and round up so that they resemble the original
pith and cortex cells. Cell divisions continue, especially in the pith,
increasing the tissue in the original wound gap. Simultaneously the cells
in the cambial area form a new tissue which has been called the "tumor
cambium." This layer of narrow, rapidly dividing cells lies at a certain
distance from the wound edge. It originates in the cambial area but the
stimulus to orderly cell divisions obviously diffuses to the neighboring
cells, especially toward the pith, and after a while a meristematic layer
develops around the wound. The increasing tissue in the pith pushes this
layer outward so that the normal and the tumorous meristematic areas
come to form a cylinder.
The cell divisions in the tumor cambium are not as regular and controlled as in the normal cambium. The tissue proliferation is so rapid
that the layer not only thickens abnormally but also becomes wavy. It
forms protuberances that push toward the gall surface crushing other