The paper deals with the development of
the perithecium in Nectria mammoidea. Phil, et Plowr.
The cells of the vegetative hyphae are
multinucleate.
The perithecial initial is a knot of
vegitative hyphae, and at its inception and throughout its development no trace of a structure or structures resembling archicarps can be seen.
The appearance and development of structures provisionally termed "interpolated" is described and it has been found impossible to homologise
them with known existing structures in the ascocarps
of other As corny ce te s. These structures disintegrate
prior to the appearance of the ascogenous hyphae.
These latter arise de novo from the cells
lining the base of the perithecial cavity. They
are simple binucleate structures and are not separated
by a cell wall from their parent hyphae, but are
merely prolongations of the latter. Without proliferation of these hyphae or division of their two
nuclei, the latter fuse to give the definite ascus
nucleus.
The ascus grows and is a prolongation of
the parent ascogenous hypha.
The definite ascus nucleus divides three
times, one reduction division only taking place.
The spores are formed from the ascus
cytoplasm by a free cell formation.
The spore nucleus divides and a wall
separates the two daughter nuclei which thus each
occupy a cell in the spore. The latter becomes invested by a spore wall.
The grosser features of the perithecial
development are described throughout the account in
the sequence of their occurrence in development.
Pycnidia were not found in culture but
structures which may be sterile perithecia were seen
on a few occasions.
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The variation in the literature dealing
with observations on the parasitism of Nectria
cinnabarina (Tode) Fries, is reported in the
Introduction.
These variations are concerned chiefly
with two points in the parasitism of this species
viz:- (a) the part of the host tissue primarily
attacked, and (b) the reaction of the host to attack]
The case of this fungus causing a canker of
apricot, and the various symptoms observed are dealt
with.
With a view to trying to throw some light
on the reason or reasons for this symptom
variability in the host, cultural studies and
inoculation experiments were carried out with two
strains of the fungus (1) a strain from the beech,
and (2) a strain from the apricot.
The two strains were found to be separable
on a cultural basis, while it appeared from
inoculation experiments, that the beech strain might
be a more virulent parasite of the apricot than the
apricot strain. The latter was shown to be the
cause of a canker on the apricot.
It was concluded that, as seen in the
Introduction, this fungus was capable of causing a
variability of symptoms in its host plant. The
investigation indicated that this latter might be due
to the existence of physiological strains in the
species, or be the result of the varying ages of the
host parts attacked.
A more extensive series of inoculation
experiments than that carried out during this
investigation, would probably decide which of these
two factors was the causative one. Both, however,
may be concerned.
