Study of Spirogyra uitida. 223 



from the band. Such tests, however, yielded only negative 

 results. The substance corresponds in every respect with 

 a true fat. It persists in the cell through the primary 

 stages, and even after the contents have balled off, dark 

 spots are seen on treating with osmic acid. These show a 

 tendency to collect in the interior of the mass. 



The relation of the tannin to the conjugating cell is very 

 complex. The quantity of tannin in the normal healthy 

 cells is extremely variable, and the different amounts ob- 

 served in the conjugating cells were so wide-spread and so 

 unlooked for, that at first it seemed impossible to formulate 

 them. Close study of the plant at all stages indicates the 

 following history of the tannin content for the conjugating 

 cell. 



It has been noticed that rapid division always precedes 

 conjugation. After this has occurred, just previous to con- 

 jugation, the quantity of tannin is very great. Iron salts 

 produce an inky-black color, while copper acetate gives 

 large masses of its characteristic brown precipitate within 

 the cell wall. This large amount of tannin does not per- 

 ceptibly alter during the growth of the first half of the 

 connecting tube. At about this stage it begins to diminish, 

 and by the time the tubes are in close proximity, the tannin 

 has almost entirely disappeared. Usually, until the tubes 

 actually meet, a slight reaction can be obtained in the tube 

 itselj. Only the merest traces are to be found in cells 

 giving or receiving the contents of an opposite cell. 

 Neither was it possible to demonstrate that one cell of the 

 pair invariably contained more tannin than its associate, 

 though frequently this seemed to be the case. 



In the two uniting threads it always happens that some 

 cells are unable to accomplish the act of conjugation, 

 though stored with the required food, and showing the 

 same preparatory peculiarities that the others show. This 

 may be due to a divergence in the direction of the two 

 threads, causing the tubes to be too short, or it may be due 

 to the fact that one thread is frequently composed of a large 



