Study of Spirogyra nitida. 243 



maintained its deep green color, and was perfectly healthy. 

 Morphologically, it was modified in that it tended to form 

 dense aggregations over the nucleus, giving the appearance 



of a protective covering. In this mass it was difficult Co 

 distinguish the individual bands. The cells were much 

 shortened — being not more than half the usual length, and 



the spiral bands were wrapped very closely around them. 



The threads grew straight upwards, the folding upon 

 itself which Spirogyra is so apt to show, and which Mann* 

 ascribes to heliotropic action, being entirely absent. JSince 

 the bine-violet rays are those which, more than any others, 

 induce heliotropic curvature, this fact is noteworthy. 

 Further mention will be made of it when the growth under 

 the vel low-orange is discussed. 



Green glass. — Under green glass the results were more 

 abnormal. Orange, yellow, green and a little blue cannot, 

 apparently, compensate for the absence of the strong red 

 rays. In twenty-four hours from the time of the begin- 

 ning of the experiment, the chlorophyll bands had begun 

 to break down, while at the end of forty -eight hours many 

 cells had the pyrenoids connected by only a fine green 

 filament. The spiral position of the bands was quite lost, 

 and the remains lay hap-hazard in the cell. The condition 

 of the cells composing a single thread varied much. Some 

 were quite free from starch, others had unusually large 

 starch grains around clear large pyrenoids. In those cells 

 which were free from starch iodine frequently, though not 

 invariably, produced a violet coloration, closely approach- 

 ing the color obtained in like manner when the plant was 

 grown under violet light. 



Another phenomenon, which was observed only a few 

 times, was the presence of oil droplets, on or close to the 

 chlorophyll. These were blackened by osmic acid, were 

 soluble in the usual solvents for fats, and behaved in every 

 respect like the droplets observed in the plant when pre- 



*Proc. Bot. Soc. Edin. Vol. 18. 



