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WHOLE SPORES
COLOR:
Orange-brown (0-20-60-0) to dark orange-brown
(0-10-60-0), with many between these two extremes (0-40-100-0). Contents of
juvenile spores are dense, so spores appear much more
opaque than at maturity.
SHAPE: Globose
to subglobose, more rarely ellipsoid or irregular.
SIZE DISTRIBUTION:
80-160 µm, mean = 109 µm (n = 102).
SPORE WALL:
Two layers (L1 and L2), the outer layer continuous with
the wall of the neck of the parent sporiferous saccule and sloughing;
the inner layer becoming the spore wall, rigid, and ornamented.
L1:
A hyaline layer that is continuous with the wall of the saccule neck; 0.5-0.8
µm thick; usually present on spores with saccules attached and sloughed when
saccules become detached or collapse and degrade.
L2: A layer consisting of yellow-brown (0-30-100-0) to darker
yellow-brown (0-30-100-10) sublayers (or laminae) that is seamlessly encloses
the spore contents. Thickness ranges from 2.4-4.4 µm thick (mean of 3.3 µm).
At maturity, the pore between spore and saccule neck is closed by continuous
sublayers of this layer, with remnants of the saccule neck appearing as a ridge
and leaves a wide scar (or cicatrix) on the spore surface.
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GERMINAL WALLS: Two flexible hyaline inner walls (gw1 and gw2) are readily seen in broken spores.
GW1: Often gives the appearance of being a single layer because the two layers present tend to be adherent; near equal thickness; together1-2 µm thick.
GW2: Consisting of two layers that also usually are adherent. L1 is 0.5-0.8 µm thick, with granular excrescence (or "beads") that tends to become dislodged and float away with applied pressure. These "beads" are stabilized after preservation in formalin, but otherwise may be absent on mounted spores within a few months of storage. L2 is plastic enough that it has been termed "amorphous". It can range in thickness from 4-12 µm in PVLG-based mountants, depending on amount of pressure applied to it while breaking the spore; staining red-purple (20-80-20-0) to dark red-purple (40-80-60-0) in Melzer's reagent. This layer is nonreactive in youth and gradually becomes more reactive as differentiation is completed.
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Arbuscules generally stain lightly in trypan blue, making observation of fine architecture difficult. Intraradical hyphae and vesicles stain with much more varying intensity, from almost invisible to quite dark. Infection units appear to be patchily distributed in red clover, sudangrass, and corn, with oblong to irregular vesicles often forming in localized clusters.
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Not reported by Wu and Liu (1995) and not observed in pot cultured spores to date. It is assumed that a germ tube arises from a hyaline "germination orb" that forms on the innermost germinal wall (gw2).
So far, this species has been found only in Taiwan. It has been cultured in standard potting mixes as well as in aeroponic chambers (Wu, personal communication). This species is somewhat unique in the genus in the robustness of the saccule neck wall, so that saccules often remain attached or when detached, a highly visible proximal cicatrix remains.
Wu and Liu (1995) do not report the granular nature of the surface of the outer layer of the innermost germinal wall (gw2). This is significant, because it appears to be a highly conserved property shared by all species of Acaulosporaceae.
Wu, C.-G. and Y.-S. Liu. 1995. Glomales of Taiwan: V. Glomus chimonobambusae and Entrophospora kentinensis, spp. nov. Mycotaxon 53:283-294.