The chief factor in the production of the footpath socies from the grassland community is the mechanical effect of treading and puddling; this exerts a selective influence on the grasses. The dominants are zoned according to intensity of treading. Under dry conditions where no puddling occurs, treading alone produces little change. Trifolium repens does not resist treading as much as do the grasses, and hence occupies only the outer zone of the footpath.[long dash]The interstices of flagged paths and sidewalks are dominated by Poa pratensis.[long dash]The characteristic flora of a cart-track or gateway community owes its existence to severe disturbance and churning of the ground. During summer the disturbed area is populated by annuals or by seedling perennials (chiefly Plantago major and Poa pratensis). The undisturbed areas between or around the disturbed region are populated by perennials which may resist severe treading, but cannot survive disturbance and churning of the ground during winter. All the spp. are ill adapted to compete for light, and the habitat offers illumination without competition; it also favors spp. which germinate comparatively late in spring.