In _Alectoria_, haptera are formed at the tip of the thallus filament as an apical cone-like growth from which hyphae may branch out and penetrate any convenient object. A species of this genus was thus found clinging to stems of _Betula nana_. Apical haptera are very frequent in _Cladonia rangiferina_ and _Cl. sylvatica_, induced here also by contact. These two plants, as well as several species of _Cetraria_, tend, indeed, to become entirely epiphytic on the heaths of the _Calluna_ formations. Haptera similar to those of _Alectoria_ occur in _Usnea_, _Evernia_, _Ramalina_ and _Cornicularia_ (_Cetraria_). In _Evernia prunastri_ var. _stictoceros_, a heath form, the fronds become attached to the stems and branches of _Erica tetralix_ by hapteroid strands of slender glutinous hyphae which persist on the frond of the lichen after it is detached as small very dark tubercles surmounted, as Parfitt[370] pointed out, by a dark-brown grumous mass of cells. Plug-like haptera may be formed at the base of _Cladoniae_ which attach them to each other and to the substratum. The brightly coloured fronds of _Letharia vulpina_ are attached to each other in somewhat tangled fashion by lateral bridges or by fascicles of hyphae dark-brown at the base but colourless at the apices, exactly like aerial adventitious rhizinae. They grow out from the fronds generally at or near the tips and lay hold of a neighbouring frond by means of mucilage. These haptera are evidently formed in response to friction. Haptera along with other lichen attachments have received considerable attention from Galløe[371]. He finds them arising on various positions of the lichen fronds and has classified them accordingly. After the haptera have become attached, they increase in size and strength and supply a strong anchorage for the plant; the point of contact frequently forms a basis for renewed growth while the part beneath the hapteron may gradually die off. Haptera are more especially characteristic of fruticose lichens, but Sernander considers that the rhizinae of foliose species may function as haptera. They are important organs of tundra and heath formations as they enable the lichens to get a foothold in well-lighted positions, and by their aid the fronds are more able to resist the extreme tearing strains to which they are subjected in high and unsheltered moorlands. F. STRENGTHENING TISSUES OF STRATOSE LICHENS