6
AECD-3446(App. )
responses induced by 2, 4-D and 2, 4, 5-T are very similar to those of the other
growth substances, except that they are more marked in degree.
In some cases,
there is stimulated cell proliferation and lateral root production, while in
other cases, there is greater cambial activity and the formation of thick-walled
xylem cells (29).
Viruses in plants usually do not affect the meristematic regionse
"The
continued normal functioning of the meristem of the growing points and cambium
regions of most virus-affected plants indicates that if viruses are present in
the meristem they rarely cause appreciable direct injury to this type of tissue"
(2).
dn exception to this statement is the virus-produced tumor reported by
Kelly and Black (20).
This tumor arose chiefly in the pericyclic region of roots
and stems and consisted of groups of distorted tracheids surrounded by meristema-
tic cells and parenchyma interspersed with phloem.
Description of Tumors on Ipomoea tuba. =
The tumors varied from small wart-like tubercles at the nodes to large
contorted masses 5-6 centimeters in circumference (Figures 5a and 5b)-
The tumors
were yellowish-green in color, but the leaves produced on the newer growth above
were normal in color.
As has already been stated, leaves sometimes arose from
the tumorous masses themselves, indicating at least partial recovery.
Histology. -
Whole tumors were brought to the laboratory in FAA.
Pieces of the tumor
tissue were dehydrated and cleared in an alcohol-chloroform series and inbedded
in "Tissuemat."
They were sectioned serially at 151 and stained by Comant's
Quadruple stain schedule.
Sections of the stem of normal plants grown from
seed in the greenhouse were fixed in FAA and either stained and sectioned as
above or sectioned at 20u on a freezing microtome and stained with safranin and
fast green.