Myxophycece 315 



these movements are most conspicuous, and they become more 

 active under those conditions which cause an increase in the 

 activity of protoplasm, such as an augmentation of the temperature 

 or of the intensity of the light. It has been stated by Cohn l and 

 by Correns 2 that the movements only take place when the filaments 

 are in contact with a solid body, and it seems probable that, at all 

 events in certain species, contact with a solid body or with the 

 surface film of water is actually necessary for the performance of 

 these movements. The motion consists of a slow creeping or 

 gliding of the entire filament which at the same time slowly 

 rotates around its axis, and this is often accompanied by a slow 

 oscillation of the extremity of the filament. It must be distinctly 

 understood, however, that the movements are not of precisely the 

 same character in all the species of the genus. The filaments of 

 some species secrete a small quantity of a colourless jelly, and 

 it was to this secretion of mucilaginous matter that Siebold, 

 Engelmann, and others attributed the movements. There is, 

 however, quite as much probability in the explanation put forward 

 by Hansgirg that the movements are due to osmotic changes. 



In Arthrospira the movements consist of a general bending 

 of the spiral filaments or a slow oscillation of their extremities. 

 These movements are more vigorous than those of Oscillato ri<i, 

 spasmodic and jerky, and I have not observed any rotation of the 

 spiral filaments. 



In the genus Spirulina, in which the filament is also twisted 

 into a close spiral, the movement consists of a rotation around the 

 axis of the spiral, with a slight propulsion through the water. 

 In Sp. turfosa Buln., this rotatory motion is relatively rapid. 



Many of the Oscillatoriacere emit a very disagreeable odour, 

 and ponds and ditches which contain quantities of Oscillatoria 

 often give off bad smells. This is attributed by Jackson and 

 Ellms 3 to the decay of highly nitrogenous organic matter, in which 

 partially decomposed sulphur and phosphorus compounds play a 

 large part. 



The phenomena of ' water-bloom ' and the ' breaking of the 

 meres ' are due to the sudden and often periodical appearance of 

 large quantities of a few species of the Myxophyceee, and the 



1 Cohn in Archiv fiir mikr. Anat. 11(57, p. 48. 



2 Correns in Berichte Deutsch. Bot. Ges. 1896, xiv. 



3 Jackson & Ellms in Technul. Quarterly, 1897, x. 



