Certain spp. of Polytrichum, because they readily establish themselves on bare soil areas of fine detritus or sand and because they produce dense growths of rhizoids, are often important stabilising agents on such substrata. P. pilijerum and P. juniperinum are frequently successful pioneers on sandy soils in the English Midlands because they readily produce long branched etiolated shoots when covered by blown sand. The effect of a covering of sand on P. pilijerum is demonstrated, also that the presence of the sand stimulates the production of rhizoids on the etiolated shoots.