308 FKES1I-WATER ALG^E OF THE UNITED STATES. 



smaller ones is 3.5-4 /<. Color of larger tricliome aeruginous 

 granular ; smaller ones the same as sheath, which is light 

 yellow to brownish red, smooth when young, becomes fibril- 

 lose with age. 



Syn. Hydrocoleum heterotrichum,JLg. , Inctctis homceotricha, (Kg. 

 Thur.) Kirch. 



Plate CCV, figs. 2, 3, two younger filaments : fig. 4, an 

 older filament showing the two forms of trichonies ; sheath 

 smooth ; fig. 5, more advanced in age, the sheath becomes 

 lamellate and fibrillose. 



From swamp near Bethlehem, Pa. 



Genus 103, OSCILLAKIA, Bosc. 



Filaments straight, or slightly curved, rarely circinate and 

 spirally convolute except in very young condition ; branchless 

 and without a discernible sheath. Color mostly bright aeru- 

 ginous, but often changes to violet or steel blue. All, in good 

 vegetative state, are more or less motile and involved in a thin 

 matrical mucilage ; joints disc-shaped in front view. 



The mystery of the oscillating and creeping movements of the 

 Oscillaria has evoked many theories, but none, hitherto, have re- 

 ceived a general approval. Some of the most recent thoughts 

 come from Dr. A. Hansgirg, Professor in the Royal University 

 of Prague, several of which we quote, before adding a simple 

 idea of our own, and that perhaps not quite original. His first 

 experiments were made to obtain the relationship of the move- 

 ments to light. The filaments of OsciUaria FroeUclm^ placed in 

 complete darkness were found to have lost on the second day 

 their mucilaginous envelope and to have sunk to the bottom of 

 the vessel. The twisting and creeping movements, however, 

 continued until the seventh or eighth day, becoming gradually 

 weaker. The more sensitive filaments of 0. aerugmeo-coerulia 

 lost their power of motion more rapidly. 



In direct sunshine the movements were more lively than in 

 diffused day-light. An increase of temperature of the water 

 also promoted the rapidity of the movements. 



The separate filaments of the same cluster move with different 

 degrees of rapidity, depending not only on the warmth and light 

 but also on the age of the filament. The quality of the water, 

 whether river, spring, or stagnant water has also an effect. 



The twisting, oscillating or nodding movements, the author 

 believes to be due, not to their growth, but to osmotic changes 



