PROTOPHYTA. 113 
filaments. Some are amber-colored, some brownish, some 
bluish-green. The species of Oscillaria (Fig. 49, B) are 
mostly dark-green filaments collected into felt-like masses 
floating on the surface of the water, or growing on wet 
earth or the wet sides of watering-troughs, etc. A pecu- 
liarity of these plants is their power of oscillating from 
side to side, while at the same time they move forward. 
In this manner they are enabled to travel considerable dis- 
tances. 
232. In Rivularia the filaments are generally arranged 
radially in little rounded masses. One of these (Rivularia 
fluitans) is often very abundant in lakes and slow streams, 
the little floating greenish balls being a millimetre or less 
in diameter. Other species occur as green slimy masses, as 
large as pin-heads, on the stones and stems of water-plants 
in ponds and brooks. 
233. Related to the foregoing, but probably not falling 
within this class, are the bright-green “ Green Slimes” which 
have been known under the name of Protococcus. They 
are invariably one-celled plants, and the cells are much 
larger than in any of the preceding. They occur com- 
monly on damp walls and rocks and the sides of flower- 
pots in greenhouses and conservatories, and in wet weather 
on wooden walks and the roofs and sides of houses. 
234, One species of Protococcus (P. nivalis) is the noted 
Red-snow Plant which in the high north latitudes often 
covers the snow, giving it a reddish color. It also occurs 
on the mountain-tops in lower latitudes. Although really 
a green plant, its color is reddish in one of its stages. 
235. In their modes of multiplication these species of 
