PD organization within pits is indicated with small cartoons in each graph. Pits themselves are distributed on a regular triangular grid. Within pit fields, the nearest neighbour distance between PDs (120 nm by default) is independent of the number of PDs per pit field. (A-C) is represented as a function of total PD density (the total number of PD entrances per unit of cell wall area) for: a varying number of PDs per cluster (as indicated by line type, (A), for different PD length (B, solid lines: isolated PDs, dash-dotted lines: 7 PDs per cluster, red colour indicates : 100 nm, cyan for 200 nm, blue for 500 nm) and for different PD spacing within clusters (C, shown for clusters of 7 PDs with centre-to-centre distance as indicated by line type and colour). Cluster sizes 5, 6, and 19 are indicated with blue lines for readability (A,D). For comparison, for non-clustered but randomly distributed PDs is also indicated. (D) The impact of increasing the number of PDs per cluster on as a function of cluster density (the number of pit fields per unit of cell wall area). Lines show the fold increase of when increasing the number of PDs per cluster from one to the number indicated by the line type (same as in A). Lines are terminated where of clusters meets of isolated PDs at the same total PD density. Beyond that, calculation results are no longer reliable because clusters get too close and the impact of clustering on could be considered negligible. (A-D) Default parameters: = 100 nm, = 120 nm, = 12 nm.