Origin of Second Spiral in Spirogyra lutetiana 



Grace A. Hill, 

 University of Washington, Seattle. 



Filaments 30-36 /x in diameter; cells 3-7 diameters long; chloroplast 



1, broad, dentate, dark green, making 3-7 turns in the cell; fertile cells 

 sometimes swollen, sometimes cylindrical; spores polymorphous, either 

 globular, ellipsoid, oblong, cylindric-ellipsoid, pyriform or reniform, yel- 

 lowish at maturity, 2-4 diameters long, 30- iO /x in diameter. (Collins.) 



The plants examined were collected in the basin of an old fountain 

 on the campus of the University of Washington in December, 1916. The 

 filaments were only 20-32 /u, in diameter. The chloroplasts were 12-15 [x 

 wide, and deviated from the transverse by an angle of 10°-30°, usually 

 about 20° in normal cells. The plants differed from the description above 

 in that the cells were 3-12 times as long as wide; the chloroplasts made 

 3-8.5 turns per cell; and rather frequently there were 2 chloroplasts per 

 cell (Figs. 8, 10, 12). The greater number of turns might be expected 

 from the longer cells. 



A study of the origin of the second spiral showed that sometimes 

 there was only 1 when there appeared to be 2, because it doubled back 

 the whole length of the cell (Fig. 6). In a few instances, through doubling, 

 there appeared to be 3 spirals (Fig. 5) ; but in such cases the cell was 

 unusually short. It may be that doubling back is due to the chloroplast 

 growing too rapidly for the cell. Various stages of it were observed (Figs. 



2, 3, 4, 6). Apparently the cell as a rule eventually breaks where it dou- 

 bles. It appears that breaking at the return bend may occur at any pe- 

 riod (Fig. 9). Thus one source of the rather frequent occurrence of 2 

 spirals is explained ; by division such a cell obviously forms more cells with 

 2 spirals. 



The cells of S. lutetiana seem to be more or less subject to irregulari- 

 ties. Not infrequently a small piece was found broken from the main 

 chloroplast (Fig. 7). More commonly the spirals were broken near the 

 middle (Fig. 11), whereupon the 2 broken ends passed each other (Fig. 

 12). Thus 2 spirals were formed. 



If a cell like that in figure 6 were to divide before the chloroplast 

 breaks at the bend, there would probably be 2 chloroplasts in one of the 



(247) 



