LICHENS. 107 
The connexion between the two layers of the 
lichen, alluded to in the preceding paragraph, is 
not the result of simultaneous individual growth 
in one organism, but is due to parasitism. The 
colourless filamentous tissue of the corticolous layer 
or hypha is supposed to be a kind of spawn or 
mycelium belonging to some obscure fungus 
living parasitically upon the coloured cellular 
portion or gonidia, whose resemblance to certain 
unicellular or rudimentary algz has been already 
observed. Schwendener, who first suggested this 
startling idea, remarks that he saw the threads of 
the hypha of lichens penetrating the fronds of 
different primitive algz, such as nostoc, growing 
beside them, encompassing the filaments of the 
alga with a net-work which swelled and ex- 
tended itself at the points of contact, and thus 
burst the filaments of the alga enclosed into 
small fragments which became transformed into 
gonidia, “As the result of my researches,” he says, 
“all these lichen-growths are not single plants, not 
individuals in the ordinary sense of the word; 
they are rather colonies, which consist of hundreds 
and thousands of individuals, of which, however, 
only one plays the master, whilst the rest, in 
perpetual captivity, prepare the nutriment for 
themselves and their master. This master is a 
fungus of the class of Ascomycetes, a parasite 
