340 
IVEY F. LEWIS AND CONWAY ZIRKLE 
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18. Schmitz, F. Die Chromatophoren der Algen. (Abstr, in Just's Bot. Jahresb. 10^: 
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21. Tilden, J. Minnesota algae. Vol. i. Minneapolis, 19 10. 
22. West, G. S. British freshwater algae. Cambridge, 1904. 
23. , Cambridge botanical handbooks. Vol. i. Algae. Cambridge, 19 16. 
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EXPLANATION OF PLATES 
Plate XX 
These photographs were taken with a Gordon's photomicro camera. In figure i, a 
Zeiss 2 mm. water-immersion objective and a Bausch and Lomb no. 10 eye-piece were used; 
in figures 2-12, a Zeiss 1.5 mm. oil-immersion objective and a Zeiss compensating ocular 
no. 6. The tube length was 160 mm. Magnification, X 400. 
Fig. I. Living cells showing cell division. 
Fig. 2. Fixed in picric acid and stained in Heidenhain's haematoxylin. 
Fig. 3. Same as figure 2. 
Fig. 4. Fixed over a water bath with picric acid and stained with anilin-gentian violet. 
Fig. 5. Fixed and mordanted with pyrogallic acid-ferrous sulphate, stained with 
anilin-gentian violet. 
Fig. 6. Fixed as in figure 5. Not stained. 
Fig. 7. Fixed as in figure 5. Stained with anilin-safranin. 
Fig. 8. Stained by Van Ermengen's osmic acid-silver nitrate process. 
Fig. 9. Fixed with tannic acid, stained with anilin-gentian violet. 
Fig. 10. Fixed with a solution of pyrogallic acid and ferric bromide in ether, stained 
with safranin. 
Fig. II. Same as figure 10. 
Fig. 12. Fixed in i part formalin and i part saturated solution of gentian violet in 
95 % alcohol, counterstained in Heidenhain's haematoxylin. 
Plate XXI 
Figs. 13-17. Living material showing increase in size and cell division. X 1070. 
Fig. 18. Resting stage. X 1600. 
Figs. 19-27. Stages showing fragmentation of chromatin and changes in pyrenoid. 
X 1600. 
Figs. 28-34. Stages showing nuclear and cell division. X 1600. 
Figs. 35-38. Stages showing reassembling of chromatin. X 1600. 
Fig. 39. Cells connected by stalks. X 1600. 
