OSCILLATORIACE^. 97 



filament may be readily separated. They have been described as sporidia; but obser- 

 vations on their germination are wanting. Minute zoospores have been observed in 

 some. Besides the ordinary sheath which encloses each medullary column, a suppli- 

 mentary sheath is found in some genera, as in Microcoleus, enclosing a considerable 

 number of separately sheathed filaments. The origin of this general sheath has not 

 been observed. It probably originates as a simple filament, whose endochrome divides 

 and subdivides longitudinally, thus forming a number of filaments within the body of 

 the older one, whose walls continue to enlarge, being fed by the matter of the contained 

 filaments. This appears, at least sometimes, to be the case : in other cases probably 

 the investing sheath is formed of exuviae and dead filaments. 



Many plants of this Order are celebrated for exhibiting peculiar movements resembling 

 those of animals. Some have a rapid progressive and regressive movement, by which 

 they can change their place, rising or falling in the water ; others, while remaining 

 nearly in one place, move from side to side, describing an arc. The genus Oscillatoria 

 is so named from the pendulum-like movements of its filaments. Species of this genus 

 are to be found in most pools of stagnant water, and their peculiar movements may be 

 easily observed. These plants occur, when fully developed, in floating, skin-like, slimy 

 pellicles, of a deep green or blackish or blueish colour and gelatinous substance. If a 

 small portion of the floating scum be placed in a cup of water, and allowed to remain 

 for some hours at rest, its edges will become finely fringed with delicate, radiating 

 threads, which extend further and further, from hour to hour ; and if the experiment 

 be continued for a day or two, in warm weather, the whole surface of the water will be 

 coated with a thin layer of filaments, which will spread till stopped by the dry edges of 

 the cup. These filaments were at first contained within the gelatinous matrix, and 

 have merely spread out, not grown, from it, by means of their peculiar movements. 

 These movements are of three kinds : — first, there is the oscillating movement ; one 

 end of the thread remaining nearly at rest, while the other sways from side to side, 

 sometimes describing nearly a quarter of a circle in a single swing. Secondly, the tip 

 of the filament has a minute movement, bending from side to side, like the head of a 

 worm : and thirdly, there is an onward movement, probably the result of the tAvo 

 former. It is this latter which causes the filaments to radiate and spread out from the 

 edges of the stratum. If a minute portion of a living Oscillatoria be placed in water, 

 under a moderately high magnifying power, all these movements can be seen without 

 trouble. They vary in vividness, however, in difierent species, some being active, and 

 some sluggish ; and also according to the state of the weather, being most rapid in 

 warm weather. Some of the species are furnished with minute cilia at the extremities, 

 but these do not seem to take part in the motion. 



Oscillatoriaceoe are found in all parts of the world, and under a great variety of 

 circumstances. Not very many, with the exception of the Lyngbyce and Calothrices, 

 are marine ; the great proportion are found in fresh water. Several occur in hot-springs, 

 even in the Geysers of Iceland ; and others inhabit water highly charged with minei'al 

 salts or gases. Some are found on damp soil ; others under the spray of cascades, and 

 on the gates of canal-locks and about mill-dams. Few pieces of stagnant fresh water 

 are free from them ; but rivers and streams are equally furnished, and broad lakes are 







