MORPHOGENESIS OF CROWN
GALL
59
belong, for instance, the tumors on the tomato and the pea (Kupila, 1958),
the tobacco (Kupila, \963), and the broad bean (Therman, 1956). The
other type has been named the unorganized type and is represented by
the galls on the sunflower (Kupila, 1958).
The development of the teratoma-type galls can be summarized as
follows: In the early stages of the development the features typical of
the normal wound reaction are visible at the inoculated site. The cells
tend to enlarge and then start to divide in one direction so that files of
cells heading toward the wound edge are formed. The broken ends of
tracheids and sieve tubes near the wound edge become closed as a result
of the enlargement of the surrounding cells. Tracheid strands differentiate
from the vessels toward both the pith and the cortex. Similarly, phloem
reacts by sending new strands in different directions. The cells of the stele
react most vigorously by dividing; the reaction of the cells of the pith
and the cortex depends on the plant species.
The effect of the crown gall inoculation on the tissue organization
becomes evident in about a week. The cells that do not divide keep
enlarging so that a number of giant cells make their appearance. The
division planes in the continuously proliferating tissues cease to be
parallel. As a result the orderly arrangement of the cell files disappears.
The division pattern in different parts of the tumor changes so that
among the relatively slowly, but continuously, dividing cells, centers of
smaller and more rapidly dividing cells are formed. These growth centers
appear first in the outer parts of the tumor, and when the galls enlarge
new centers arise continuously in the periphery. Growth centers can also
appear deeper in the tissue. Division of the innermost cells in these
centers seems to continue for a limited time only. Soon a few or even a
single cell differentiates into a tracheidlike structure, the neighboring
cells follow, and a woody core originates inside the center. Simultaneously
the outer cells continue to divide so that a cambiumlike area originates
around the center. Sieve elements also differentiate in the outer parts of
these growth centers. Large cells that have never divided during the
tumor development are still visible in the tissue.
When the tumor ages the proportion of the differentiated cells in the
tissue increases continuously. Eventually thin strands seem to connect all
the woody cores of the growth centers to the better organized central
bundles so that the lignified cells form an interconnected network.
Phloem tissue is also abundant in the galls. It appears either in the
bundles or as thin, one-celled strands in all parts of the gall. The directions of differentiation of the tracheid and sieve-element strands in an
GALL
59
belong, for instance, the tumors on the tomato and the pea (Kupila, 1958),
the tobacco (Kupila, \963), and the broad bean (Therman, 1956). The
other type has been named the unorganized type and is represented by
the galls on the sunflower (Kupila, 1958).
The development of the teratoma-type galls can be summarized as
follows: In the early stages of the development the features typical of
the normal wound reaction are visible at the inoculated site. The cells
tend to enlarge and then start to divide in one direction so that files of
cells heading toward the wound edge are formed. The broken ends of
tracheids and sieve tubes near the wound edge become closed as a result
of the enlargement of the surrounding cells. Tracheid strands differentiate
from the vessels toward both the pith and the cortex. Similarly, phloem
reacts by sending new strands in different directions. The cells of the stele
react most vigorously by dividing; the reaction of the cells of the pith
and the cortex depends on the plant species.
The effect of the crown gall inoculation on the tissue organization
becomes evident in about a week. The cells that do not divide keep
enlarging so that a number of giant cells make their appearance. The
division planes in the continuously proliferating tissues cease to be
parallel. As a result the orderly arrangement of the cell files disappears.
The division pattern in different parts of the tumor changes so that
among the relatively slowly, but continuously, dividing cells, centers of
smaller and more rapidly dividing cells are formed. These growth centers
appear first in the outer parts of the tumor, and when the galls enlarge
new centers arise continuously in the periphery. Growth centers can also
appear deeper in the tissue. Division of the innermost cells in these
centers seems to continue for a limited time only. Soon a few or even a
single cell differentiates into a tracheidlike structure, the neighboring
cells follow, and a woody core originates inside the center. Simultaneously
the outer cells continue to divide so that a cambiumlike area originates
around the center. Sieve elements also differentiate in the outer parts of
these growth centers. Large cells that have never divided during the
tumor development are still visible in the tissue.
When the tumor ages the proportion of the differentiated cells in the
tissue increases continuously. Eventually thin strands seem to connect all
the woody cores of the growth centers to the better organized central
bundles so that the lignified cells form an interconnected network.
Phloem tissue is also abundant in the galls. It appears either in the
bundles or as thin, one-celled strands in all parts of the gall. The directions of differentiation of the tracheid and sieve-element strands in an