OF THE OSCILLATORLE. 
7 (\ 
CHAPTER VIII. 
OF THE OSCILLATORIAS. 
Of the members of this family, the Lyngbyse and the 
species of Leptothrix which float on the surface of the 
water may all be prepared in precisely the same way as 
was recommended for the Confervas in the previous chap- 
ter. Those like Phormidium, which form filmy masses, 
will be treated of presently. But the genus Oscillatoria 
itself requires a peculiar mode of preparation. The 
individuals embraced in this group dwell by preference on 
mud at the bottom of shallow ponds and ditches ; though 
frequently, on a sudden rise of the water, they break away 
from the soil and float, appearing like a cloudy film 
radiating from a centre. All have a disagreeable odour, 
which clings to them long after they have been deposited 
in the herbarium. They vary much in colour; the 
common tint is an asruginous green, darker or lighter in 
different species. Others are steel-blue or even brown — as, 
for instance, Oscillatoria Frohlichii in many of its habitats. 
During the process of drying, they change colour, owing to 
the influence of the oxygen in the atmosphere, their tints 
gradually becoming brighter and more intense. This is 
well seen in the last-named species, which is usually of a 
deep brown during life, but which after death, and while 
drying, assumes first a blackish-green tint, and then a steel 
■colour’. 
The family takes its name from a property peculiar to 
some of them, but not common to all, of spontaneously 
oscillating or waving gently backwards and forwards, like 
a very slow-moving pendulum. To whatever cause this 
mysterious movement may be due, the fact itself is of 
