LICHEN ALGAE 65 



E. NON-GONIDIAL ORGANISMS ASSOCIATED WITH LlCHEN HYPHAE 



Bonnier 1 made a series of cultures with lichen spores and green cells 

 other than those that form lichen gonidia. In one instance he substituted 

 Protococcus botryoides for the normal gonidia of Parmelia (Xanthoria) 

 parietina; in another of his cultures he replaced Protococcus viridis by the 

 filamentous alga Trentepohlia abietina. In both cases the hyphae attached 

 themselves to the green cells and a certain stage 

 of thallus formation was reached, though growth 

 ceased fairly early. Another experiment made 

 with the large filaments of Vaucheria sessilis met 

 with the same amount of success (Fig. 34). The 

 germinating hyphae attached themselves to the 

 alga and grew all round it, but there was no ad- 

 vance to tissue formation. 



Cultures were also made with the protonema 

 of mosses. Either spores of mosses and lichens 

 were germinated together, or lichen spores were 

 sown in close proximity to fully formed proto- 

 nemata. The developing hyphae seized on the 

 moss cells and formed a network of branching 

 anastomosing filaments along the whole length of 

 the protonema without, however, penetrating the 

 cells. If suitable algae were encountered, proper 

 thallus formation commenced, and Bonnier con- 

 siders that the hyphae receive stimulus and 

 nourishment from the protonema sufficient to 

 tide them over a considerable period, perhaps until the algal symbiont is 

 met. An interesting variation was noted in connection with the cultures of 

 Mnium kornum*. If the protonema were of the usual vigorous type, the 

 whole length was encased by the hyphal network; but if it were delicate and 

 slender, the protoplasm collected in the cell that was touched by hyphae 

 and formed a sort of swollen thick- walled bud (Fig. 35). This new body 

 persisted when the rest of the filament and the hyphae had disappeared, 

 and, in favourable conditions, grew again to form a moss plant. 



F. PARASITISM OF ALGAE ON LICHENS 



A curious instance of undoubted parasitism by an alga, not as in 

 Strigula on one of the higher plants, but on a lichen thallus, is recorded 

 by Forssell 3 . A group of Protococcus-\\k& cells established on the thallus 



1 Bonnier 1888 and i88o 2 . * Bonnier 1889. 3 Forssell 1884, p. 34. 



Fig. 34. Germinating hyphae of 

 Lecanora subfusca Ach. , grow- 

 ing over the alga Vaucheria 

 sessilis DC., much magnified 

 (after Bonnier). 



S. L. 



