MORPHOGENESIS OF CROWN GALL
61
cells. The cells in the tumor cambium often elongate tangentially and
sometimes, especially in the protuberances, radially, thus differing from
the normal cambium. Cells outside the tumor cambium look parenchymatous and keep dividing.
Numerous tracheids and sieve elements differentiate in the sunflower
crown gall, but the pattern of tissue differentiation does not resemble
that observed in the teratoma-type gall. A number of the derivatives of
the tumor cambium on the side of the pith form spiral or reticulate
thickenings as a consequence of which a layer of distorted wood originates. The formation of wood is considerable in the upper part of the
gall where some strands of twisted tracheids may extend toward the gall
surface. The proximal part of the gall contains more regular rows of
lignified cells. It seems possible that the strong lignification of the cells
in the distal part of the gall results from a blockage of the nutrient
transportation.
Phloem elements differentiate on the surface side of the tumor
cambium, forming a layer of relatively organized phloem with a number
of sieve elements. An abundance of sieve elements running as singleelement strands may also be scattered in all parts of the tumor.
The tumors described above were induced with a moderate bacterial
strain. It is possible that the difference between the two types of galls is
not as clear when a virulent strain is used. Thus the description of the
crown gall on the sunflower stem by Stonier (cf. Braun and Stonier,
1958) differs somewhat from that given above.
Riker (1923b) has described oriented divisions taking place around the
bacteria-containing intercellular spaces. The same phenomenon has been
observed by Stonier (Braun and Stonier, 1958), but not by Kupila (1958)
and by Bopp and Leppla (1964).
A somewhat different picture of the gall development on the stem has
been presented by Bopp and Leppla (1964) in Kalanchoe
daigremontiana.
The tumors were followed for 90 days. The difference between the
sterile wounded tissue and the crown gall tissue became evident in 4
days. At this time the cells in the connective tissue formed more or less
oriented rows, but in the cortex the divisions were less polarized. After
a while a number of single cells showed exceptionally vigorous proliferation which resulted in the formation of a number of thin-walled cells
inside the thicker walls of the mother cells—a phenomenon described
also in a number of earlier studies (e.g., Riker, 1923b; Kupila, 1956, 1958;
Therman, 1956). As a result of cell proliferation and cell growth, a tissue
of medium-sized cells originated and increased continuously in amount.
61
cells. The cells in the tumor cambium often elongate tangentially and
sometimes, especially in the protuberances, radially, thus differing from
the normal cambium. Cells outside the tumor cambium look parenchymatous and keep dividing.
Numerous tracheids and sieve elements differentiate in the sunflower
crown gall, but the pattern of tissue differentiation does not resemble
that observed in the teratoma-type gall. A number of the derivatives of
the tumor cambium on the side of the pith form spiral or reticulate
thickenings as a consequence of which a layer of distorted wood originates. The formation of wood is considerable in the upper part of the
gall where some strands of twisted tracheids may extend toward the gall
surface. The proximal part of the gall contains more regular rows of
lignified cells. It seems possible that the strong lignification of the cells
in the distal part of the gall results from a blockage of the nutrient
transportation.
Phloem elements differentiate on the surface side of the tumor
cambium, forming a layer of relatively organized phloem with a number
of sieve elements. An abundance of sieve elements running as singleelement strands may also be scattered in all parts of the tumor.
The tumors described above were induced with a moderate bacterial
strain. It is possible that the difference between the two types of galls is
not as clear when a virulent strain is used. Thus the description of the
crown gall on the sunflower stem by Stonier (cf. Braun and Stonier,
1958) differs somewhat from that given above.
Riker (1923b) has described oriented divisions taking place around the
bacteria-containing intercellular spaces. The same phenomenon has been
observed by Stonier (Braun and Stonier, 1958), but not by Kupila (1958)
and by Bopp and Leppla (1964).
A somewhat different picture of the gall development on the stem has
been presented by Bopp and Leppla (1964) in Kalanchoe
daigremontiana.
The tumors were followed for 90 days. The difference between the
sterile wounded tissue and the crown gall tissue became evident in 4
days. At this time the cells in the connective tissue formed more or less
oriented rows, but in the cortex the divisions were less polarized. After
a while a number of single cells showed exceptionally vigorous proliferation which resulted in the formation of a number of thin-walled cells
inside the thicker walls of the mother cells—a phenomenon described
also in a number of earlier studies (e.g., Riker, 1923b; Kupila, 1956, 1958;
Therman, 1956). As a result of cell proliferation and cell growth, a tissue
of medium-sized cells originated and increased continuously in amount.