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Details
A type
of review of already published observations of cell wall modifications
in elms affected with the Dutch elm disease and, at the same time, of
links with the preceding two papers are presented herein. Thus, slightly
affected vasicentric cells in the secondary xylem reacted by depositing
new lucent or opaque layers that were of greater density beneath pit
membranes. Walls of tyloses present in these tissues were characteristic
of young tissues and when they were altered, which was often the case,
it was similarly as in those, in relation with opaque matter. A
noticeable thickening of pit membranes and even of vessel layers
occurred in some cases, which seemingly was associated with lighter
attacks of adjoining cells. Degradation of pit membranes of
half-bordered pits was noticeable as their shredding into opaque bands
and granules, in close contact with F-cells or with opaque vessel wall
linings. Pronounced wall thickenings in adjoining parenchyma cells could
again be observed. Similar wall modifications also occurred in recently
deposited cells in the cambium and phloem regions next to invaded
vessel elements, this being most outstanding following recurrent
infection. Wall ingrowths stemming from the native cell walls or of
their thickened portions were noticeable in some cells. These wall
features, even in pith cells, were again observed to be associated with
the occurrence of opaque masses or bands of opaque matter. This matter,
which in many cases extended from the cell periplasm into its content,
displayed pinhole-like elements, whose occurrence will be described at
greater length in the following articles.
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