Lichen rhizinae, distinguished by Reinke[367] as “aerial rhizinae,” are more or less characteristic of all the species of _Parmelia_ with the exception of those belonging to the subgenus _Hypogymnia_ in which they are of very rare occurrence, arising, according to Bitter[368], only in response to some external friction. They are invariably dark-coloured, rather short, about one to a few millimetres in length, and are simple or branched. The branches may go off at any angle and are sometimes curved back at the ends in anchor-like fashion. The _Parmeliae_ grow on firm substances, trees, rocks, etc., and the irregularities of their attaching structures are conditioned by the obstacles encountered on the substratum. Not unfrequently the lobes are attached by the rhizinae to underlying portions of the thallus. In the genus _Gyrophora_, the rhizinae are simple strands of hyphae (_G. polyrhiza_) or they are corticate structures (_G. murina_, _G. spodochroa_ and _G. vellea_). They are also present in species of _Solorina_, _Ricasolia_, _Sticta_ and _Physcia_ and very sparingly in _Cetraria_ (_Platysma_). _c._ HAPTERA. Sernander[369] has grouped all the more distinctively aerial organs of attachment, apart from rhizinae, under the term “hapteron” and he has described a number of instances in which cilia and even the growing points of the thallus may become transformed to haptera or sucker-like sheaths. The long cilia of _Physcia ciliaris_ occasionally form haptera at their tips where the hyphae are loose and in active growing condition. Contact with some substance induces branching by which a spreading sheath arises; a plug-like process may also be developed which pierces the substance encountered—not unfrequently another lobe of its own thallus. The long flaccid fronds of _Evernia furfuracea_ are frequently connected together by bridge-like haptera which rise at any angle of the thallus or from any part of the surface. The spinous hairs that border the thalline margins in _Cetraria_ may also, in contact with some body—often another frond of the lichen—form a hapteron, either while the spermogonium, which occupies the tip of the spine, is still in a rudimentary stage, or after it has discharged its spermatia. The small sucker sheath may in that case arise either from the apex of the cilium, from the wall of the spermogonium or from its base. By means of these haptera, not only different individuals become united together, but instances are given by Sernander in which _Cetraria islandica_, normally a ground lichen, had become epiphytic by attaching itself in this way to the trunk of a tree (_Pinus sylvestris_).