178 BOTANICAL GAZETTE. [ August, 
tact with the hyphe rests on laboratory cultures in which it 
is claimed that, if the germinating spores of lichens be 
brought in contact with pure gonidia, the hyphe at once 
grow more rapidly, and the gonidia also begin to multiply. 
But this increase of the gonidia is not necessarily a sign that 
the conditions of growth have become more favorable. When 
the black knot fungus attacks a branch of the plum tree the 
parenchymatous cells increase, anda knotis formed; andthe 
better when free than when shut up in the lichen thallus. 
They are neither benefited nor destroyed, but they are weak- 
Protococcoid gonidia of the larger lichens, which are more 
“uxurlant when growing free on rocks and bark. It is 1m- 
possible to regard the Stigonema gonidia, distorted and 
broken up by the hyphe, as in a more flourishing condition 
than when free, 
. algo-fungal theory is not that they assume that the gonidia, 
ts ee of the hyphe. From the facts which I have Maite 
~ 18 plain that they are injured, and, if the injury is less than 
i Most Cases of parasitism—which may be due to the fact 
f lichens grow more slowly than those © 
ee tn evertheless an injury, and we must recog- 
: ze in lichens not a case of symbiosis or mutual parasitism, 
uf a case of true parasitism with a minimum of injury to the 
