312 MICROSCOPIC FORMS OF VEGETABLE LIFE. 



mordial colls, usually lying together in bundles or in strata, some- 

 times quite free, and sometimes invested by a gelatinous matrix. 

 The endochrome which they contain usually exhibits some degree 

 of transverse striation, as if breaking up into short segments by 

 the division of the tube into cells ; but this division is never 

 perfected by the formation of complete partitions ; and the fila- 

 ments ultimately break up into distinct joints, the fragments of 

 endochrome, which are to be regarded asgonidia, usually escaping 

 from their sheaths, and giving origin to new filaments. These 

 plants are commonly of some shade of green, often mingled, 

 however, with blue ; but not unfrequently they are of a purplish 

 hue, and are sometimes so dark, as, when in mass, to seem nearly 

 black. They occur not only in fresh, stagnant, brackish, and 

 salt waters (certain species being peculiar to each), but also in 

 mud, on wet stones, or on damp ground. Their very curious 

 movements constitute the most remarkable feature in their his- 

 tory. These are described by Dr. Harvey 1 as of three kinds ; 

 first, a pendulum-like movement from side to side, performed by 

 one end, whilst the other remains fixed so as to form a sort of 

 pivot ; second, a movement of flexure of the filament itself, the 

 oscillating extremity bending over first to one side and then to 

 the other, like the head of a worm or caterpillar seeking some- 

 thing on its line of march ; and third, a simple onward move- 

 ment of progression. " The whole phenomenon," continues Dr. 

 H., "may perhaps be resolved into a spiral onward movement of 

 the filament. If a piece of the stratum of an Oscillatoria be 

 placed in a vessel of water, and allowed to remain there for some 

 hours, its edge will first become fringed with filaments, radiating 

 as from a central point, with their tips outwards. These fila- 

 ments by their constant oscillatory movements, are continually 

 loosened from their hold on the stratum, cast into the water, and 

 at the same time propelled forward ; and as the oscillation con- 

 tinues after the filament has left its nest, the little swimmer 

 gradually moves along, till it not only reaches the edge of the 

 vessel, but often, as if in the attempt to escape confinement 

 continues its voyage up the sides, till it is stopped by dryness. 

 Thus in a very short time, a small piece of Oscillatoria will spread 

 itself over a large vessel of water." This rhythmical movement, 

 impelling the filaments in an undeviating onward course, is 

 evidently of a nature altogether different from the truly sponta- 

 neous motions of Animals ; and must be considered simply as 

 the expression of certain vital changes taking place in the inte- 

 rior of the cells. It is greatly influenced by temperature and 

 light, being much more active in warmth and sunshine than in 

 cold and shade ; and it is checked by any strong chemical agents. 

 The true Generation of Oscillatoriacece is as yet completely un- 

 known ; and it does not seem at all unlikely that these plants 

 maybe the " motile" forms of some others, which, in their " still" 



1 " Manual of British Marine Algae," p. 220. 



