94 MORPHOLOGY 



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 1 , 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 Soforina, Ricasolia, 

 Sticta and Physcia and very sparingly in Cetraria (Platysma). 



c. HAPTERA. Sernander 2 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 en- 

 countered 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). 



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 



1 Bitter 1901. 2 Sernander 1901. 



