TEN YEARS’ PROGRESS IN LICHENOLOGY. 283 
The author describes various growth forms of the lichen 
thallus as exhibited in Peltigera canina, Physcia parietina, 
foliose forms, Usnea barbata, and Cladonia sylvatica, fruticose 
forms, and claims that such raise doubts as to whether the 
fact of the association of fungus and alga has anything to do 
with the matter of form ; and adds further, “ that such doubts 
are confirmed when one realizes that not one of the form factors 
is anything new after all, as they are in fact only a repetition of 
the commonest common-place factors of the somatic organiza¬ 
tion of algae as seen in modern sea-weeds.” From this it is in¬ 
ferred that the fugus symbiont, after association with the alga, 
continues to develop a growth form similar to that exhibited 
by its ancient ancestry which, as Dr. Church asserts, was evolved 
in the sea. “ It is to the sea that one must look for the analogue 
of any specialised lichen-thallus.” 
A subsequent paper, “ The Lichen as a Transmigrant,” by 
the same author (25), although not published within the period 
now under review, has been included, owing to its intimate 
association with the one entitled “ Lichen Symbiosis.” 
The reader is reminded that in an ordinary Fucoid the photo¬ 
synthetic chlorophyll cells are in close contact with the external 
food solution, for thev constitute a thin brown external film 
surrounding the mechanical tissue of the central axis. “Stripped 
of the outer layers, the whole plant reduces to a system of 
hyphal strands as an interwoven mechanical tissue ot descending 
hyphae, to all intents and purposes the mycelium of a 
fungus-axis.” The more internal tissues having previously 
lived at the expense of the surface layers and not feeling the 
effect of the change of environment so readily would continue 
to live for a time. 
“ A higher fungus of the land is in short a skinned sea-weed 
. . . of which, on the death and decay of the older meta¬ 
bolic and autotrophic surface layers the exposed internal tissues 
continue their existence at the expense of the soluble carbohyd¬ 
rates of the standing and non-aerated medium.” 
The writer’s view is that “ the main series of higher Eumycetes 
are derived from stripped sea-weeds, which emerge from the 
water. . . . The Lichen represents the case of similar 
simple or branched algal somata, remaining denuded of auto¬ 
trophic tissue in standing pools, and, hence, soon smothered 
