This layer degrades or sloughs as the spore dehisces from the saccule neck. This layer may be hard to see with brightfield optics because it is close in color to L2 and when adherent, boundaries between layers are harder to see. Neither layer produces a reaction in Melzer's reagent. Breakage of the pedicel usually results in detachment of spore from saccule neck. Hyaline when fully developed, light pink with opaque contents when young.
Full size is attained prior to initiation of spore differentiation.
Only with a compound microscope are details of colonization evident. Infection units rarely overlapping, often patchily distributed in sorghum roots. No intraradical vesicle formation was evidenced in the pot culture host examined. All of these species have three layers in the spore wall, with those of A. colossica and A. laevis almost identical. The innermost layer of the spore wall of A. koskei is distinct in producing a dextrinoid reaction in Melzer's reagent.