NELLIE CARTER: FRESHWATER ALGÆ, 53 
about 2 or 3 mm. high. Microscopic examination shows that it consists of 
a felt of Scytonema filaments bound together by anastomosing fungal hyphe. 
The erect tufts also consist of a number of parallel Scytonema filaments 
closely adherent to each other, bound together and completely surrounded 
by a loose mat of hyphæ. The undulating lines in the sheath of the 
alga figured by Schmidle and thought by him to be due to the peculiar 
structure of the sheath itself, were very conspicuous also in the New 
Caledonian specimens, and alter careful observation it was proved beyond 
all doubt that these undulating lines are caused by the hyphae of the 
fungus, which are placed side by side round the algal filament to form a 
complete sheath. Further, the horizontal lines joining the undulating longi- 
tudinal lines are the septa of the hyphæ. The alga with its sheath of fungal 
hyphe is seen in optical transverse section in text-fig. 1, C. The undu- 
lating arrangement of the hyphæ along the alga is most remarkable, and it 
is difficult at first to believe that the undulating lines are really due to a 
fungus, until at intervals irregularities may be observed, in which the hyphæ 
forming the sheath of the alga may separate from each other, and become 
apparent as ordinary hyphe branching off into the ordinary free mycelium 
(text-fig. 1, D& E). At intervals also, the undulating hyphe on the alga 
can be seen giving rise to branches, some of which may join up with the mat 
of mycelium which surrounds each bundle of algal filaments (text-fig. 1, B). 
Only those hyphe forming the sheath of the Scytonema filament are wavy ; 
the mycelium which is free from the alga consists of normal straight hyphæ. 
It is difficult to find a reason for the undulating nature of the hyphe sur- 
rounding the alga, unless that by the hypha being thus dovetailed into each 
other, a stronger union is effected by them, and a firmer sheath results. It 
is noteworthy in this connection that the fungus sheath persists with violent 
treatment long after the enclosed Scytonema filament has disappeared, and 
that it breaks as a whole, transversely without the hyphæ showing any signs 
of separating from each other longitudinally. No trace of the fungal 
hyphe actually penetrating the algal cells was observed.  Scytonema 
Hieronymi seems to be a most interesting case of lichen formation. 
SCYTONEMA DENSUM (A. Br.) Bornet. River Dumbéa; in small clear 
pool. 810. Europe, America. 
S. ALATUM (Carm.) Borzi (Petalonema alatum Berk.). Forma tricho- 
matibus gracilioribus, cellulis diametro circiter 3-plo longioribus ad apicem 
subquadratis. Mont Humboldt ; on wet rocks or roots. 10454. Pie la; 
on wet serpentine soil, 865. Europe, America. 
TOLYPOTHRIX BYSSOIDEA (Harv.) Kirchn. Specimen without locality. 88. 
Europe, Borneo, W. Indies. 
