AECD-3446 (App. )
5
there is a stimulatory effect on cells in a meristematic or plastic condition
(11).
As a result, there is cell enlargement or cell division or both, and the
affected parts fail to differentiate into the characteristic tissues of the normal
plant organ on which the gall is formed.
The view is generally held that chemical
secretions of the larvae are primarily responsible for the proliferations (6)
although Rahn (26) makes a novel suggestion that radiation from the larvae may
have some effect.
There is a close analogy between the insect gall and the develop-
ment of adventitious buds (7).
On red currants, one of the mites produces a some-
what swollen bud, or a dense growth of buds which do not develop normally (L)o
Insect galls are not systemic, although evidence of systemic disturbance due to a
multiplicity of insect bites has been presented in one case (25).
Even in this
instance, the effect did not extend for more than one or two internodese
A number of workers have reported tumors on plants following the applica-
tion of indoleacetic acid (5, 8, 31).
When the histology of such tumors was
studied by Kraus, Brown and Hamner (21) it was found that the cells of the endo~dermis were especially responsive.
to adventitious roots.
Root histogens developed and later gave rise
Over the vascular bundles long proliferating strands of
vascular tissues developed from endodermal derivatives.
These frequently en-
larged sufficiently to rupture the tissues exterior to them.
chyma, and xylem proliferated greatly.
have been much the same.
Cambium, ray paren-
The responses reported for other plants
Some investigators claim that the galls produced by
indoleacetic acid and other organic acids are similar to those brought about by
actual infection with the crown-gall organism (5, 22, 23).
Im all oases of tumors
‘and overgrowths produced by growth substances, there is a marked proliferation
of tissues which have already differentiated.
The reports of adventitious shoots
in cabbage (12), in Nicotiana hybrids (14), and in Geranium (30) indicate that
somewhat normal recovery from growth substances is possiblee
The histological
DOE ARCEYVa