Summary..1. Bare places of the desert bear a rich cover of lower plants, i.e. of lichens.2. Lichens may be of great use in defining the floristic characteristic of steppe and desert.3. With the help of lichens it is possible to prove the identity of the desert in Egypt and in Southern Palestine.4. A similarity of the desert in Algeria to those in Egypt and Palestine was established.5. With the help of lichens the different nature of the steppe in Southern Russia from that in Palestine and Mesopotamia was proved.6. Lichens may decide whether certain plant formations in arid regions have to be regarded as desert or steppe.7. TerrestrialDiploschistesspecies were found to possess an economic value by indicating the steppe or arable nature of the soil upon which they grow.