30 CONSTITUENTS OF THE LICHEN THALLUS 



Parmelia acetabulum, another corticolous species, formed only a minute 

 thallus about $ mm. in diameter, but entirely identical with normally growing 

 specimens. 



(2) Pleurococcus. 



Lecanora {Rinodina) sophodes, sown on rock in 1883, reached in 1 886 a 

 diameter of 13 mm. with fully developed apothecia. 



Lecanora ferruginea and L. subfusca after three years' culture formed 

 sterile thalli only. 



Lecanora coilocarpa in four years, and L. caesio-rufa in three years formed 

 very small thalli without fructification. 



(3) Trentepohlia (Chroolepus). 



Opegrapha vulgata in two years had developed thallus and apothecia. 

 The control culture of the spores formed, as in nature, a considerable felt of 

 mycelium in the interstices of the bark, but no pycnidia or apothecia. 



Graphis elegans. Only the beginning of a differentiated thallus was 

 obtained with this species. 



Verrucaria muralis (?)^ gave in less than a year a completely developed 

 thallus. , ■ . 



Bonnier also attempted cultures with species of Collema and Epkebe, but 

 was unsuccessful in inducing the formation of a lichen plant. 



H. Hymenial GONIDIA 



Reference has already been made to the minute gre,en cells which were 

 originally described by Nylander^ as occurring in the perithecia of a few 

 Pyrenolichens as free gonidia, i.e. unejitangled with lichen hyphae. Fuisting' 

 found them in the perithecium of Polyblastia {Staurothele) catalepta at a very 

 early stage of its development when the perithecial tissues were newly 

 differentiated from those of the surrounding thallus. The gonidia enclosed 

 in the perithecium differed in no wise from those of the thallus: they had 

 become mechanically enclosed in the new tissue; and while those in the 

 outer compact layers died off, those in the centre of the structure, where a 

 hollow space arises, were subject to very active division, becoming smaller 

 in the process and finally filling the cavity. Winter's* researches on similar 

 lichens confirmed Fuisting's conclusions: he described them as similar to 

 the thalline gonidia but lighter in colour and of smaller size, measuring 

 frequently only 23 /a in diameter, though this size increased to about 7 /a 

 when cultivated outside the perithecium. 



StahP sufficiently demonstrated the importance of these gonidia in 



1 Bonnier was probably experimenting with an Arthopyrenia. Verrucaria species combine with 

 Protococcus or according to Chodat with Coccobotrys gen. nov. 



2 Nylander 1858. ^ Puisting 1868, p. 674. ^ Winter 1876, p. 264. ^ Stahl 1877. 



