Cytology and Movements of the Cyanophycece. 307 



diffused, but gradually forms into large angular masses of 

 irregular shape. 



(7) Motility. 



The power of movement among the Cyanophyceae is 

 quite marked in some forms, and is practically the only 

 distinguishing feature between some genera. In Oscillaria, 

 the movements are most marked, and may be divided into 

 three classes: (a) Creeping or forward movement of the 

 whole trichome, by which it propels itself through the water 

 in a serpentiform fashion. (&) An oscillating movement 

 throughout the whole trichome, which gives the name to 

 the genus. This movement might also be divided into two : 

 (i) the general oscillation, and (2) the more rapid flexion 

 of the extreme end of the trichome which usually closes 

 the oscillation, (c) A spirally twisting movement which 

 accompanies the oscillation. Cylindrospermum and several 

 others of the Cyanophycese exhibit the first or creeping 

 movement above mentioned, while the hormogonia of those 

 forms which bear them are free-swimming, sometimes with 

 a twisting motion as in Nostoc {yj). Such movements 

 among plants have been considerably studied, principally 

 on Diatoms, and from these, generalizations have been 

 made to include other organisms. Several theories are 

 advanced to account for the phenomena, but most of them 

 seem untenable. Pritchard (64) has given a very good 

 review of all of the theories held by different authorities 

 concerning the cause of the movements in diatoms, prior 

 to 1861, therefore it will be unnecessary to more than glance 

 at a few of them here and note their bearing upon the ques- 

 tion of locomotion in the Cyanophycese. 



Naegeli (58) explained the motion as caused by osmotic 

 currents between the cells and the surrounding water. He 

 says : "Since in the course of their process of nourishment 

 they take up and secrete fluid stuffs, so the cell must come 



