LICHEN GONIDIA 



35 



instances the cells of the alga are clasped by the fungus which causes the 

 disintegration of the filament. The cells lose their bright yellow or reddish 

 colour and are changed in appearance to greenish lichen gonidia; but no 

 penetration by haustoria has ever been observed in Trentepohlia. 



Bachmann's 1 study of a similar gonidium in a calcicolous species of 

 Opegrapha confirms Frank's results. The algae had pierced not only between 

 the looser lime granules but also through a crystal of calcium carbonate, and 

 occupied nests scooped out in the rock by means of acid formed and excreted 

 by their filaments. When association took place with the fungus, the algal 

 cells were more restricted to a gonidial zone; but some of the cells, having 

 been pushed aside by the hyphae, had started new centres of gonidia. On 

 contact with the hyphae there was a tendency to bud out in a yeast-like 

 growth. 



In the thallus of the Roccelleae, the algal filament, also a Trentepohlia, is 

 broken up into separate cells, but in the Coenogoniaceae, whether the 

 gonidium be a Cladophora as in Racodium,or a Trentepohlia as in Coenogonium, 

 the filaments remain intact and are invested more or less closely by the 

 hyphae. 



A somewhat different type of association takes place between alga and 

 fungus in Strigula complanata, an epiphyllous lichen more or less common 

 in tropical regions. Cunningham 2 , who found it near Calcutta, described the 

 algal constituent and placed it in a new genus, Mycoidea (Cephaleuros). It 

 forms small plate-like expansions on the surface of the leaf, and also pene- 

 trates below the cuticle, burrowing between that and the epidermal cells; 

 occasionally, as observed by Cunningham, rhizoid-like growths pierce deeper 

 into the tissue into and below the epidermal layer. Very frequently, in the 

 wet season, a fungus takes possession of 

 the alga and slender colourless hyphae 

 creep along its surface by the side of the 

 cell rows, sending out branches which 

 grow downwards. Marshall Ward 3 de- 

 scribed the same lichen from Ceylon. He 

 states that the alga may be attacked at 

 any stage, and if it is in a very young con- 

 dition it is killed by the fungus; at a 

 more advanced period of growth it con- 

 tinues to develop as an integral part of 

 the lichen thallus, but with more frequently divided and smaller cells. 

 Vaughan Jennings 4 observed Strigula complanata in New Zealand associated 

 with a closely allied chroolepoid alga Phycopeltis expansa. He also noted the 

 growth of the fungus over the alga breaking up the plates of tissue and 



1 Bachmann 1913. 2 Cunningham 1879. 3 Ward 1884. 4 Jennings 1895. 



32 



Fig. 13. Outer edge of Phycopeltis expansa 

 Jenn., the alga attacked by hyphae and 

 passing into separate gonidia x 500 (after 

 Vaughan Jennings). 



