A. Lorrain Smith and J. Ramsbottom. 295 
IS PELVETIA CA N ALICULA TA A LICHEN? 
Bv A. Lorrain Smith, F.L.S., 
and J. Ramsbottom, M.A. 
I N intellectual as well as in spiritual matters we are apt to take 
much for granted until some question suddenly make us halt 
and give an account of the faith that is in us. A startling suggestion 
as to the nature of lichens has recently been made with regard 
to the well-known alga Pelvetia can all cul at a. In the present volume 
of the New Phytologist (pp. 33-42), Prof. G. K. Sutherland describes 
four new species of Pyrenomycetes inhabiting the thallus of this 
common brown seaweed. Concerning one of them, Mycosphcerella 
Pelvetice, he states that the very slender intercellular mycelium 
permeates every portion of the thallus, branching freely and forming 
a loose net-like web surrounding the cells, but apparently doing 
“not the slightest trace of injury to the host.” The mycelium 
penetrates into the young receptacles of the alga and there 
commences to fruit. As the ascospores are set free at the same 
time as the oospheres, the fungus is enabled to continue the 
association and to find its way into the intercellular spaces at a 
very early stage of the development of the alga. Examination of 
Pelvetia from different parts of the country, and from herbarium 
specimens, showed that the fungus seems to occur in every thallus. 
The author states’ that this “ symbiotic species is of special interest 
as its occurrence throws a new light on Pelvetia , opening the 
question whether it should be regarded as a lichen rather than an 
alga.” Without entering into the question as to whether the fungus 
which lives in the mucilage layers of the cell walls of the alga and 
is practically restricted in its fruits to the presumably more richly 
nutrient region of the neighbourhood of the algal conceptacles, is 
in truly symbiotic association with the alga, and assuming the 
author’s view to be correct, can the compound organism Pelvetia- 
Mycosphcerella be placed in the class Lichenes ? Or, in general, must 
every case of symbiosis between a fungus and an alga be considered 
a lichen? Tournefort (El^mens de botanique, 1694) was the first 
to classify lichens as such, and systematists since his day have 
always been clear as to which organisms should be placed in the 
group. It is true that there are difficulties in some cases as to 
whether certain species should be placed amongst lichens or fungi, 
just as at times there is difficulty in deciding between fungi and 
1 Loc. cit., p. 34. 
