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Nostoc:
a genus of
cyanobacteria
characterised by more or less long chains formed by a single
row of rounded cells. In some genera (e.g. some
Leptogium
species) the chains are very
short, consisting of a few cells only.
Ocular chamber
(of asci): the ascus is
bitunicate
, the two layers separate at the tip leaving an
empty space (see
tholus
), this space is concave with respect to the inner part of the ascus.
Orbicular
(of thallus): more or less circular in shape.
Ornamented
(of spores): spore
wall
not smooth. Ornamentation in some groups e.g.
Buellia
can
be microrugulate, striate etc.
Ostiole
: pore-like opening situated at the top of a
perithecium
or
of
pycnidia
, through which the
propagules escape.
Oval
(of spores): egg-like, the convex part lying more or less in the centre, symmetrical with
respect the two axes.
Ovoid
(of spores):
see
oval
.
P
(reagents): Para-phenylendiamine in alcoholic solution (of short duration!). It is also possible
to prepare
P
in water solution: e.g. 1 g of Para-phenylendiamine, 10 g of Natrium sulphate in
100 ml water. This substance, although still utilised e.g. for hair dying, might be
carcinogenic. It should be used with great care (especially avoid to breath it under the
microscope!). Teachers should not endorse its use by students, unless coupled with a lesson
on the use of potentially dangerous substances, and with the corresponding measures.
Paraphyses
(singular: paraphysis)
:
sterile
hyphae
in the
hymenium
, forming a palisade within
which the
asci
are interspersed. They may be simple or ramified, in some case they are
anastomosing
; the upper cells, sometimes inflated and most often pigmented, form the
epihymenium
. The true paraphyses always start from the base of the
hymenium
. See also
paraphysoids
and
periphyses
.
Paraphysoids
: structures resembling paraphyses, but ontogenetically originating from the
hymenial tissue between the
asci
. They are usually thin, abundantly branched and
anastomosing
, e.g. in
Arthonia
. In our keys, this term is sometimes used in the descriptions,
being substituted by the term
paraphyses
in the dichotomies.
Paraplechtenchymatous
(of sections): a fungal tissue (section!) consisting of more or less
isodiametrical, rounded to angular cells. See also:
plectenchyma
,
prosoplechtenchymatous
.
Parasitic
: this term is used here in a very broad, often incorrect sense: it refers both to truly
parasitic fungi growing on lichens, and to the so-called “
parasymbiontic
” lichens, i.e. those
which regularly start their life-cycle on other lichens, without being true parasites; in fact,
having a photobiont layer, they are autotrophic; their “parasitism” probably consisting in
“stealing” photobionts from the host lichen. More research is necessary to clarify the
complex relations between “parasymbiontic” lichens and their hosts.
Parasymbiontic
: see
parasitic
.
Parathecium
(of apothecia): proper
margin
, formed only by fungal
hyphae
. Not used in our
keys, but sometimes present in the descriptions.
Peltate:
plate-like, with a single attachment point from the centre of the lower surface.
Periclinal
(of hyphae): parallel to the surface.
Periphyses
(singular: periphysis):
hyphae
resembling
paraphyses
, produced near the
ostioles
of
perithecia
. They are mostly short and thin, hair-like. In our keys, this term only appears in
the descriptions.
Periphysoids:
this term is used by some authors to designate
paraphyses
-like structures of
pyrenocarpous
lichens, developing from the upper part of the
pyrenium
, and growing
downwards. In our keys the term was not used consistently: it should be best regarded as a
synonym of
paraphyses
.
Perispore
(of spores): a colourless gelatinous layer around
spore
, visible in microscopic
sections. See also
halonate
.
