60 
INDEX LICHENUM BRITANNICORUM. 
181 L. squamulosa, Dealc. 
182 L. mesoidea, Nyl. 
183 L. premneoides, Nyl. 
184 L. subimbricata, Nyl. 
( To be continued .) 
Bibliography. 
Lichens of the Isle of Man. By W. H. Wilkinson, “ Midland 
Nat.,” Nov., 1893, p. 245. 
We have in this number indicated a first instalment of the list. 
Each species is accompanied by a short diagnosis, also habitat and 
locality. Leighton’s “ Lichen Flora of Great Britain ” has been 
followed in the arrangement and descriptive portion. There is 
very little, if any, advantage in reproducing specific characters 
already existing in a manual, whereas original notes, supplement- 
ing the comparatively meagre characters given in the work 
referred to, would have been of value. The only figure given is 
presumably intended to represent the spore of Collema pulposum. 
although we are not told so. Underneath the said figure occurs 
the following : u Spore '02 x *01 mm.” The figure, however, is 
exactly one-third longer than wide. Which is right ? 
On the Structure and Biology of Lichens. By Dr. A. Minx, 
“ Abhandl. Zool. Bot. Gesell.,” Wien, 1893, p. 377. 
The authors explanation of the dual nature of lichens differs 
from the view propounded by Schwendener, in considering that 
the relation of gonidia and lichen matrix is not one of parasitism, 
but what is termed syntrophism. The gonidium element may be 
looked upon as a louger (Miether), inhabiting the lichen matrix 
as a place adapted to its requirements, and giving something of 
value to its host in return. The influence exercised by the lodger 
on its host varies in different species, and is usually most pro- 
nounced where the syntrophism is of long standing. Many 
lichens never have gonidia during any stage of their develop- 
ment. 
The above idea is in the main in accord with the generally 
received notion, that the relation between the gonidia and the 
lichen is one of mutualism or symbiosis. It is true that Schwen- 
dener, who first propounded the idea of the dual nature of lichens, 
considered the gonidia as being seized upon by the fungus, thus 
implying parasitism, but this view has been corrected long ago, and 
the two elements constituting a lichen are now considered to be an 
alga and a fungus, living together in a state of mutualism. 
Dr. Minx, however, appears to consider that lichens, without 
gonidia, are distinct from fungi. This difference we should be 
pleased to see satisfactorily explained. 
