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8
AECD-3446 (App. )
pletely undifferentiated but elongated cells, which must serve as conducting
tissue, to phloem with an apparent organization (in cross section) into sieve
tubes and companion cells.
However, no sieve plates were observed.
The xylem
elements are very much shortened with reticulate or spiral thickenings.
The
conducting tissues are rather regularly arranged in a cylinder around a central
pith in each individual swelling of the multiple tumor.
differentiates.
An internal phloem
The available material was not well fixed for cytological pur-
poses, but the nuclei appeared normal.
The parenchyma contains cluster crystals
especially near the lactiferous ducts and starch grains are particularly abun-
dant nee outermost layers of parenchyma.
The lactiferous ducts are not well
developed as in the normal stem and there appear to be no functioning secretory
cells.
Aside fron the proportionately small amount of coductive tissue, the
tumors appear histologically surprisingly normal.
There are no giant cells, the
tissues maintain a regular arrangement, and there is no excessive proliferation
of any one tissues
There is simply a general "ground mass" of parenchyma with
relatively little xylem and phloem.
The striking histological feature of the tumors is the large number of
growing points or primordia most of which fail to continue development.
primordia show a wide range from normality.
These
In normal primordia, apical growth
is retarded early and ensuing development and growth is due to intercalary
activity in addition to some wmlocalized cell division (15).
wordia, this intercalary growth seems to faile
In the tumor pri-
The procambial strands differ-
entiate into some semblance of a conductive tissue, but no new tissue seems to
develope
The meristematic cells enlarge and become parenchymatous (Figures 89
end 8b).
A phellogen must differentiate in some cases near the surface, but
very often the tissue it produces is sloughed off.
The surfaces of the pri-
mordia often appear to be suberized and some peripheral tissue sloughs off
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