CYANOPHYCEyE 443 



Engelmann (Bot. Zeit., 1879, P- 49) claims to have detected this external 

 secretion in the case of Oscillaria dubia (Ktz.). Zukal compares the 

 motion of Spirulina to that of a growing tendril, and asserts that it is 

 intimately connected with the growth of the filament. It consists of a 

 slow torsion of the entire helix round its own axis, and is the result of 

 the more rapid growth in length of the filament than of the ideal axis of 

 growth. If the motion is suddenly interrupted, the filaments become 

 for a moment quiescent, and then retreat towards the central point of 

 the movement, forming a dark green lump. Hansgirg, on the other 

 hand (Sitzber. Bohm. Gesell. Wiss.,see Bot. Centralbl., xii., 1882, p. 361), 

 considers the twisting and nodding movements to be due, not to the 

 growth of the filament, but to osmotic changes in the cell-contents ; the 

 separate cells exhibiting motion when the envelope itself is at rest. He 

 regards the movements as of the same nature as those of the sarcode in 

 the pseudopodes of Rhizopods and other Protozoa. The same observer 

 states further (Bot. Zeit., 1883, p. 831) that in the protoplasm which had 

 escaped from the broken end of a filament of O. princeps, he has observed 



Fig. 360. — Oscillaria princeps YsMch. {yi 200). (From nature.) 



a number of amoeboid cells from 9 to 12 |/ in diameter, nearly spherical 

 in form, and putting out colourless pseudopodes about twice the length 

 of the central body, and to these he attributes the motile properties of 

 the protoplasm. He believes the cause of the oscillating motion to be 

 that the internal protoplasm takes up water more rapidly, and conse- 

 quently swells to a greater extent, than the enveloping sheath, causing 

 the filament to move slowly backwards and forwards within the sheath. 

 In those species in which each filament is not invested in a separate 

 sheath, variations in the turgidity are also brought about by variations 

 in the endosmotic and exosmotic currents. Finally Schnetzler (Arch. 

 Sc. Phys. et Nat., 1885, p. 164) describes the moveaients in O. jerugineo- 

 ccerulea (Ktz.) as of six different kinds, viz. : (i) rotation of the filament 

 or of its segments round its axis ; (2) creeping or gliding over a solid 

 substratum ; (3) a swimming change of position in the water : (4) rota- 

 tion or flexion of the entire filament ; (5) sharp tremblings or concus- 

 sions ; and (6) a radiating arrangement of the entangled filaments. 



Most of the species of the typical genus Oscillaria Bosc. grow in 

 dense shmy tufts attached to other alg^e or floating bodies, th<^ filaments 

 being not more than from 2 to 6 /( in diameter : in a few species, 



