Various kinds of pathological effects of the Abutilon Mosaic Virus (AbMV) in seasonal dependency have been observed on the macroscopic as well as on the microscopic level. The annual rhythmic fluctuation of light caused by the varying length and intensity of light incidence is directly correlated with the realization of symptoms, leading to an intensification of the leaf mosaic and to an increase in the light leaf areas during the summer. These macroscopic observations are correlated with an annual change in the plastid fine structure in the mesophyll of the lightest areas of the leaf. The grana‐stroma‐organization of the plastids is completely eliminated through a reduction and disorganization in the thylakoid system during the spring and summer, restored in the autumn, and preserved over the winter. This change in the plastid fine structure is limited to the leaf mesophyll. The plastids of the leaf stem, like the plastids of non‐infected plants, do not display any change in their fine structure.

Cytological changes occurring after infection by Abutilon Mosaic Virus (AbMV) have been investigated in the host plants Abutilon sellovianum Rgl., Malva parviflora L., Malva silvestris L., and Sida micrantha Schr. Two types of virus‐like inclusions were found in different tissues: particles of 16–18 nm in diameter and elongated filaments with 6–8 nm in diameter. The particles are detectable in the nuclei (Abutilon sellovianum, Malva spec.) and cytoplasm (Malva spec.) of cells in the bundle area, and the filaments accumulate in the nuclei (Sida micrantha) and the plastids (Malva spec.) of leaf mesophyll cells.