296 A. Lorrain Smith and J. Ramsbottom. 
algte. From a comparatively early date the lichen gonidia have 
been recognized as similar to algae growing in the open, but many 
licbenologists have held in the past that such algae were free living 
gonidia, a view again seriously set forth in a recent paper by 
Elfving. 1 Most botanists, however, accept the dual nature of 
lichens as proved beyond dispute and in the lichen the algae as well 
as the fungi are equally concerned in the life of the plant. It is the 
fungus portion of the plant which produces the fruit and for that 
reason since lichens, as other plants, are classified on their 
reproductive structures which necessarily resemble fungi, some 
writers have suggested distributing lichens amongst fungal families 
according to affinities: but the algal constituent is also of importance 
in classification as it frequently determines the form of the thallus 
and can in no system be ignored. Hence the lichens are the most 
complicated class of the vegetable kingdom from a systematic 
point of view. It seems clear that lichens have been evolved on 
several lines from fungal ancestors : in fact, if Basidiolichens be 
included in the class there can be no doubt of it. Is such a poly- 
phyletic group a natural one ? It seems to us that an account of 
their structure and physiology, the lichens are just as natural a 
class as are their nearest relatives the fungi and the algae, which 
according to present orthodox theories are also polyphyletic. In 
any other scheme of classification it would seem to be necessary to 
go along the theoretical evolutionary lines rather than to group the 
organisms according to the status they have reached, and though 
theoretical classification on the lines of very hypothetical phylo¬ 
genetic trees would doubtless provide an inexhaustable series of 
interesting exercises, it would not be more scientific than the 
present grouping and would add greatly to the difficulties of 
placing individual plants. Can the dual organism Pelveha- 
Mycosphcerella be placed in this polyphyletic class ? It has long 
been known that certain brown algae have fungi parasitic in their 
thalli. For instance, Mycosplicerella Ascophylli 2 has hyphae which 
traverse the tissue of Ascophyllum nodosum in all directions and 
would appear to form a similar association with the alga, since 
Cotton states that in spite of the very abundant mycelium the host- 
plant remains quite uninjured, and that infection appears to take 
1 Untersuchungen iiber die Flechtengonidien. Acta. Soc. Sci. Fenn. 
Helsingfors, xliv, No. 2 (1913). 
* Church, A. H. A Marine Fungus. Ann. Bot. vii, p. 399 (1893). Cotton, 
A. D. Notes on Marine Pyrenomycetes. Trans. Brit. Mycological Soc. iii, 
p. 92 (1909). 
