grt] SNOW—EPIPHYTIC ALGAE 363 
tions to grow out into a long filament again, is characteristic of 
most epiphytic filamentous algae, such as Stichococcus, Hormid- 
tum, Stigeoclonium, and the following form, and in all cases, 
whether there is a specialized mode of reproduction or not, this 
phenomenon must be most instrumental in disseminating the 
plant. If in the dry epiphytic condition the plant exists in the 
unicellular state, as would seem to be the case, the cells must be 
easily blown from one locality to another, and so bring about a 
wide dissemination of the species. But during a rainy season, 
undoubtedly those single cells produce filaments which again 
become broken up into individual cells when the dry conditions 
return. 
There is but little doubt that the alternating wet and dry 
conditions of the environment in which they live are the means 
by which the polymorphic conditions of these aerial forms are 
brought about. As they change their form according to condi- 
tions, assuming the nature of either a filamentous or a unicellular 
alga, they must be regarded as transitional forms between the 
unicellular and the multicellular genera, and as such they form a 
most interesting group. 
Pirulus, nov. gen.—Alga unicellular, or forming short, fragile, 
beaded filaments. Mature cell pear-shaped, color a light green: 
chloroplast cup-shaped, with large opening at one side or at the 
smaller end; no pyrenoid present. Reproduction by budding, 
in which the smaller end elongates and is cut off by a membrane, 
after which a separation may occur or not. 
Pirulus gemmata, nov. sp.—Mature cell 0.0084-0.0112 mm. 
long and 0.0056-o.007 mm. at broadest portion. Membrane of 
cellulose; a large vacuole at the center and a nucleus present 
(4 or 8 nuclei in European form). Often forming fragile filaments 
of 12-15 cells. 
Found on epiphytic liverworts and mosses from Guatemala, also in Switzer- 
land. 
Aeronema polymorpha, nov. gen. 
Growing constantly on mosses and liverworts in certain places, 
and occasionally on the surface of flower pots in plant houses, is 
a microscopic polymorphic alga, which, according to conditions, 
