324 BOTANICAL GAZETTE [NOVEMBER 
develops on the lower side of the moss leaf and the rest of the 
lichen on the other side, the moss becoming a veritable layer of the 
lichen. In such cases the moss leaf is eventually destroyed. 
The great opportunity for the parasitizing of mosses by lichens, 
as they grow together in nature, cannot be over emphasized. 
For the most part the lichens develop on the leaves of the moss. 
Moss colonies in which apparently no lichens are present, when 
sectioned or teased out almost invariably show tiny young lichens 
developing in their leaves. Hundreds of lichens have been seen 
developing from soredial masses, but very few from spores, hence it 
is concluded that moss inhabiting lichens depend on soredia 
rather than on spores for reproduction. BoNNtER’s observations 
on the ability of lichens to germinate on, and eventually to kill moss 
protonema, have already been mentioned. Since the protonemal 
stage is a transient one, it probably does not take place in nature to 
any great extent. The germination of lichens on moss leaves is 
the rule, so far as cases where lichens eventually plaster themselves 
over the mosses are concerned. The young lichen hyphae become 
attached from their first formation. The environmental factors 
control the future appearance of the colonies. From cultures and 
field observations it is concluded that water is the dominating 
factor of the control. Almost any moss colony, apparently free 
from lichens, when grown in semimoist conditions, but occasionally 
allowed to dry out, in a few weeks will produce young lichens visible 
to the naked eye. 
If these observations are borne in mind, it is easy to see why 
so often the ideal lichen-moss-fern sequence is not carried out, 
since the sequence is broken up by lichen stages in which the 
lichens are more or less parasitic on the moss. If the rock surface 
is rough enough, visible life may be initiated by moss, and a lichen 
stage come in secondly. In any event a well established moss 
stage may be crowded out by a more or less parasitic lichen mass, 
which gives a secondary lichen stage succeeding the moss. 
S 
Lichens are able to destroy moss colonies. The destruction 
is partly due to true parasitism and partly to smothering. 
