| Arbuscules
generally stain a faint to pale blue (using trypan blue on specimens
of this website) among a greater number of species than those of Glomaceae
(in which a few species share similar staining properties). This property
also can exhibit considerable variation within the same root, varying from
almost invisible to dark blue. |
|
| Vesicles,
when they are formed abundantly, tend to be localized in regions of entry
into a root. In many instances, they form from coils of the penetration
hyphae prior to, or concurrent with, arbuscule formation. Vesicles generally
are more irregularly shaped, often appearing knobby because of surface convolutions
or oblong. They also can stain lightly, but usually appear darker than arbuscules. |
|
| Intraradical
hyphae
in entry point regions frequently are coiled and somewhat wider (4-6 µm)
than "foraging" hyphae; the latter ranges from 2-4 µm wide usually,
growing parallel to the root axis and interconnected with neighboring hyphae
by right angle or acute angle branches. Staining intensity of hyphae is
greater in entry point regions, but generally is darker than that found
in arbuscules. |
|
| Extraradical
hyphae
generally are thin (2-3 µm wide), but profuse around roots. They often remain
attached to roots in entry point regions. |
|
Species
produce asexual spores spores which:
| Originate
from the neck of a sporiferous saccule
that is formed terminally on a fertile hypha. Saccules often cease
to expand at the onset of spore formation, occurring singly and
more rarely in loose aggregates. |
|
| Usually are
sessile (no hyphal attachment) following extraction from soil because
the outer layer of the spore wall sloughs and it is continuous with
the wall the saccule neck (see #3 below). |
|
| Have an outer
layer to the spore wall (often appearing flexible
and with numerous folds because it is so thin on spores of nonornamented
species) which is continuous with the wall of the saccule neck and
which usually sloughs with age or manipulation during the extraction
procedure. |
|
| Form at least
one additional rigid layer of the spore
wall is synthesized in association with the outer
layer, but which may thicken slightly or differentiate sublayers
(= laminae) with distinct phenotypes, differing in color and surface
ornamentations when present. In the photo at right of A. spinosa,
note continuity of the outer layer and the laminae with the wall
of the saccule neck and also that the spore is borne on a pedicel
(see above). |
|
| Form
at least one germinal
inner wall. When two or more germinal inner walls
are synthesized (all but three species to date), the first inner
wall consists of one or two hyaline layers, and the second consists
of an outer "beaded" hyaline layer and an adherent inner
layer that ranges from flexible to amorphous. |
|
| Contents separate
from that of the subtending saccule neck by ingrowth of a "laminate"
layer of the spore wall, so that the spore wall eventually shows
no evidence of an opening or pore. The region of hyphal attachment
usually is evident from a ridge where the spore and hyphal wall
were connected and this round to ovoid scar is termed a cicatrix. |
|
| A germ tube
emerges from a spherical (usually) "germination
orb" (so named to indicate the absence of homology
with a similar structure named a "germination shield"
in Scutellospora). It originates from the innermost of
two or more flexible inner walls. Species with only one flexible
inner wall have yet to be shown to form a germination orb or analogous
structure. |
 |
|
