376 



BOTANY 



The simplest Lichens are the filamentous, with a filiform 

 branched thallus consisting of algal filaments interwoven with Fungus 

 hyphse. An example of such a filamentous form is presented by 

 Ephebe pubescens. This Lichen is found growing on damp rocks in 

 short, delicately branched tufts, and consists of thick, multicellular 

 filaments of the blue-green Alga Sirosiphon, whose gelatinous cell walls 

 are pervaded by the hyphse of a Pyrenomycetous Fungus. 



Pig. F.02. — Xanthoria parietina. 1, Germinating ascospore (sp) with branching germ-tube applied 

 to the Cystococeus cells (a) ; 2, thallus in process of formation, sp, two ascospores ; p, 

 Cystococcus cells. By the fusion of the hyphse in the middle of the mycelium, a pseudo-paren- 

 chymatous, cortical layer has begun to form. (After Bonnier, from v. Tavet,, x500.) 



Another group is formed by the gelatinous Lichens, whose 

 thallus, usually foliaceous, is of a gelatinous nature (e.g. Collema). 

 The Algae inhabiting the thalli of the gelatinous Lichens belong to 

 the families of the Chroococcaceae and Nostocaceae. As is characteristic 

 of the Nostocs, their cell walls are swollen, forming a gelatinous mass 

 traversed by the hyphse of the fungus. The genus Collema is an 

 example of this group. 



In both the filamentous and gelatinous Lichens the Algae and 

 Fungus hyphse are uniformly distributed through the thallus, which 

 is then said to be unstratified or homoiomeeous. The form of the 



