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AECD-3446(App. )
(Figure 9b).
It would seem that the tumors are formed because the processes of cell
elongation and intercalary growth which would normally cause a stem to increase
in length are somehow stopped.
It is interesting to note in this connection
that the growing points in the tumor tissue develop in a phyllotactic sequence
(Figure 10).
A recent paper on radiation injury in barley from absorbed P32 is of
particular interest here (24).
It was found that when a meristematic region
such as that of the root or stem tip was subjected to a constant, relatively
high level of Tadiation from absorbed P52, oell division ceased and the cells
enlarged and took on an abnormally mature appearancée
Smith and Kersten (28) working with seedlings of Vicia faba grown from
x~irradiated dry seeds found that there was little elongation in the root and
that meristematic tissue such as cambium and pericycle actually degenerated.
In their study of ionizing radiations on the broad bean root, Gray and
Scholes (13) found that after high dosages of x-irradiation (three-quarters
of a mean lethal dose of x-rays) there was a slowing down of both mitosis and
interkinesis in the meristematic region so that the rate of elongation was only
about one-fourth normale
However, in the proximal half of the meristematic
region cells continued to differentiate at roughly the normal rate but fresh
cells were not formed in the distal half to maintain the constant total number
of meristematic cells.
The effect was “in the main one of mitotic inhibition
combined with continued differentiation."
Other workers have observed injury to the meristematic regions in
x-irradiated plants.
Johnson (18) noted a change in the general aspect of
the entire plant as a result of the greater development of lateral branches.
This development of the laterals would indicate that the terminal meristem
had been injured.
In another article (19), she also states that a constant
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