Peirce[919] found that _Ramalina reticulata_ (Fig. 65), of which the fronds are an open network, was mainly distributed by the tearing of the lichen in high wind. This takes place during the winter rains, when not only the lichen is wet and soft in texture, but when the deciduous trees are bare of leaves, at a season, therefore, when the drifting thalline scraps can again catch on to branch or stem. A series of observations on the dispersal of forms of long pendulous Usneas was made by Schrenk[920]. In the Middle and North Atlantic States of America these filamentous species rarely bear apothecia. The high winds break and disperse them when they are in a wet condition. They generally grow on Spruces and Firs, because the drifting filaments are more easily caught and entangled on short needles. The successive wetting and drying causes them to coil and uncoil, resulting in a tangle impossible to unravel, which holds them securely anchored to the support. D. ERRATIC LICHENS In certain lichens, there is a tendency for the thallus to develop excrescences of nodular form which easily become free and drift about in the wind while still living and growing. They are carried sometimes very long distances, and fall in thick deposits over localities far from their place of origin. The most famous instance is the “manna lichen,” _Lecanora esculenta_, which has been scientifically examined and described by Elenkin[921]. He distinguishes seven different forms of the species: f. _esculenta_, f. _affinis_, f. _alpina_, and f. _fruticulosa-foliacea_ which are Alpine lichens, the remainder, f. _desertoides_, f. _foliacea_ and f. _esculenta-tarquina_, grow on the steppes or in the desert[922]. Elenkin[921] adds to the list of erratic lichens a variety of _Parmelia molliuscula_ along with _P. ryssolea_ from S. Russia, from the Asiatic steppes and from Alpine regions. Mereschkovsky[923] has also recorded from the Crimea _Parmelia vagans_, probably derived from _P. conspersa_ f. _vaga_ (f. nov.). It drifts about in small rather flattened bits, and, like other erratics, it never fruits. Meyer[924] long ago described the development of wandering lichens: scraps that were torn from the parent thallus continued to grow if there were sufficient moisture, but at the same time undergoing considerable change in appearance. The dark colour of the under surface disappears in the frequently altered position, as the lobes grow out into narrow intermingling fronds forming a more or less compact spherical mass; the rhizoids also become modified and, if near the edge, grow out into thread-like structures which bind the mass together. Meyer says that “wanderers” have been noted as belonging to _Parmelia acetabulum_, _Platysma glaucum_ and _Anaptychia ciliaris_.