  Arbuscular mycorrhiza (AM) is the most wide-spread plant-fungus symbiosis on
earth. Investigating this kind of symbiosis is considered one of the most
promising ways to develop methods to nurture plants in more natural manners,
avoiding the complex chemical productions used nowadays to produce artificial
fertilizers. In previous work we used the Calculus of Wrapped Compartments
(CWC) to investigate different phases of the AM symbiosis. In this paper, we
continue this line of research by modelling the colonisation of the plant root
cells by the fungal hyphae spreading in the soil. This study requires the
description of some spatial interaction. Although CWC has no explicit feature
modelling a spatial geometry, the compartment labelling feature can be
effectively exploited to define a discrete surface topology outlining the
relevant sectors which determine the spatial properties of the system under
consideration. Different situations and interesting spatial properties can be
modelled and analysed in such a lightweight framework (which has not an
explicit notion of geometry with coordinates and spatial metrics), thus
exploiting the existing CWC simulation tool.
