This section is from the book "British Wild Flowers - In Their Natural Haunts Vol5-6", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
Amongst the rock and wall plants there are few if any plants, at least amongst those enumerated here, that are adapted to dispersal of fruit or seed by the agency of animals. The absence of aquatic conditions, also, is marked by the entire absence of water-dispersed fruits or seeds.
In the exposed habitats in which a large bulk of this class of plants grow, it is, moreover, quite natural that the majority of plants growing upon rocks and walls should be adapted to dispersal by aid of the wind. It must be remembered, however, that it is necessary for plants, growing upon such limited areas as the specially suitable rocks or walls usually are, to be dispersed at no very great distance from the plant. The following are wholly or partly dispersed by the agency of the wind, viz.: Wallflower, Cheddar Pink, Field Mouse-ear, Bird's-foot, Horsevetch, Rue-leaved Saxifrage, Meadow Saxifrage (censer fruits), Navelwort, Orpine, Stonecrop, Houseleek (small seeds), Golden Rod, Mouse-ear Hawkweed, Wall Lettuce (with hairy pappus), Rampion (censer fruits), Field Speedwell, Pellitory-of-the-wall, Silky Wind Grass, Silvery Hair Grass, Flat-stalked Poa, Sand Fescue.
The rest, e.g. Yellow Fumitory, Whitlow Grass, Sandwort Spurrey, Ivy-leaved Toadflax (which buries its fruits in the crevices of the wall), have mechanisms or methods of dispersal of their own.