584 Acton . — Botrydina vulgaris , Brdbisson , 
Botrydina, , while apparently dying, was developing one or other of its two 
constituents, the conditions being unsuitable for the existence of both. 
There is some evidence that the fungus belongs to the section Helico- 
sporae of the family Mucedineae, for hyphae were observed bearing curious 
ring-shaped structures. These, on closer examination, proved to be in- 
complete rings, and suggested the first coil of a spiral conidium (Text-fig.). 
The three figures represent the beginnings of conidial stages of the fungus which forms 
one of the constituents of Botrydina. The fungus belongs to the Mucedineae. 
The alga appears to be identical with the unicellular alga which 
appeared so frequently in cultures of Botrydina in Knop’s solution, and 
which occurs commonly in damp subaerial situations. This alga I have 
recently investigated and have given it the name of Coccomyxa snbellipsoidea. 
The cells are similar in size and form. Both have a parietal chloroplast 
of similar shape, with a single pyrenoid, and both multiply by oblique 
fission. 
It is interesting to note that a culture of Coccomyxa on damp sandstone 
developed subspherical aggregates of cells which only wanted the fungal 
investment to resemble Botrydina. In this same culture fungal hyphae 
were present, but not the Botrydina-iw n gus, as the hyphae were much 
thinner and unseptate ; yet it is an interesting fact that this fungus was 
combining with the algal cells, and seemed to be forming a lichen in some 
respects analogous to Botrydina . Each algal cell was completely invested 
by the fungus, though up to the present no further stage has been noted, 
and no septa have appeared in the investing sheath. 
Conclusions. 
Botrydina vulgaris , Breb., is a primitive lichen with a more or less 
spherical thallus of small size (15-300 /x). It shows no resemblance to the 
soredial stage of a typical lichen, and is therefore possibly one of the most 
primitive types of existing lichens. It consists of an envelope of fungus 
