-18- 
Fig. i. Specimen from Crawford’s Notch, New Hampshire; central 
strand none; leaves .8 mm. long, .5 mm. wide, ovate, gradually acute to 
abruptly acuminate, acumen straight or slighly curved; leaf cells somewhat 
uniform; median broadly oval to roundish oval, nearly isodiametric. 
Fig. 2. Specimen from Northeastern Minnesota: central strand none; 
leaves differ from those of the preceding in being slightly larger, 1 mm. long, 
.6 mm. wide, more curved and longer acuminate; leaf cells larger and orbi- 
cular. 
Fig. 3. Specimen from Labrador; central strand none; leaves broadly 
ovate, 1 mm. long, .8 mm. wide, gradually acute to abruptly acuminate, acu- 
men curved; leaf cells somewhat irregular; median rhombic to oval-oblong. 
Fig. 4. Specimen from Germany; central strand rudimentary; leaves 
1.2 mm. long, .8 mm. wide: differ but little from those of the preceding; leaf 
cells somewhat longer and narrower, oval-rhombic to fusiform. 
Fig. 5. Specimen from Niagara Falls': central strand rudimentary; 
leaves ovate-lanceolate, 1.4 mm. long, .8 mm. wide, slightly curved, nar- 
rowly acuminate; median leaf cells irregularly fusiform with subsinuate 
margins ; apical cells linear-fusiform. 
Fig. 6. Specimen from Northern Minnesota; central strand present but 
small and indistinct; leaves ovate-lanceolate, 1.6 mm. long, .9 mm. wide, 
narrowly acuminate, strongly curved: median leaf cells irregular, oval- 
rhombic to oblong-fusiform; apical linear-fusiform. 
Fig. 7. Specimen from North Downs, England: central strand small, 
distinct; leaves ovate-lanceolate, 1.8 mm. long, .9 mm. wide, falcate-secund, 
long and narrowly acuminate ; leaf cells not uniform , median oval-rhombic 
to fusiform; apical long linear-fusiform. — Thuidium hystricosum from Dr. 
Mitten. 
To recapitulate: The leaves of the lowest form are ovate, .8 mm. long, 
.5 mm. wide, gradually acute to short acuminate, acumen straight or slightly 
curved, In the highest form the leaves are ovate-lanceolate, 1.8 mm. long, 
.9 mm. wide, falcate-secund, long and narrowly acuminate. The leaf cells 
in the lowest form are broadly oval, nearly isodiametric; in the highest form 
the leaf cells are irregular, the median oval-rhombic to fusiform and the api- 
cal linear-fusiform. In the lowest form the stems are without a central 
strand; in the highest form the central strand is small but distinct. In the 
intermediate forms the central strand is absent or rudimentary, and the 
median leaf cells pass from oval-rhombic to rhombic-fusiform or oblong- 
fusiform. 
The parts of the plants which exhibit a fair degree of constancy or fix- 
edness are the multiform paraphyllia, the spreading, pinnate, tapering 
branches, two-rowed on either side of the oval stem; the reddish, incrassate, 
porose basal cells of the stem leaves, the central papillae on each surface of 
the leaf cells, longer on the lower than on the upper, and the midribs about 
three-fourths the length of the biplicate leaves. 
The series here presented is one of the simplest of its kind and illustrates 
quite well the evolution of a specific type. Its individuals being usually 
