Study of Spirogyra iiitida. n-j 



dislodged from its position in the chlorophyll band, and 

 not disorganized. 



Chemical Changes in the Culls of Spirogyra Due 



to the Actiox of Monochromatic Light. 



Since 1864, when Sachs performed his now classic ex- 

 periments on the relation of bine and yellow light to plant 

 assimilation, many investigators have not only repeated, 

 but also widely extended the work done by him. 



To obtain the desired conditions, Sachs used double- 

 walled bell jars containing a saturated solution of potas- 

 sium bichromate for the yellow rays, and a solution of 

 aminoniacal copper sulphate for the blue. Others, work- 

 ing in this field, have used frames of wood, provided with 

 glass top and sides, the glasses being of the color desired. 

 Frequently light-tight, blackened boxes, having one side 

 closed by a flat bottle filled with the colored solution, are 

 employed. Engelmann obtained monochromatic light by 

 means of the micro-spectroscope, examining an algoid 

 thread in the various portions of the spectrum, and noting 

 the oxygen evolved. But by this method only small quan- 

 tities of material can be used, and the conditions, other 

 than light, are abnormal. 



Preparatory to the work done in this laboratory, a num- 

 ber of colored glasses have been tested spectroscopically, 

 but not one has been found to be monochromatic, even in 

 the broadest sense of the term. Most of the aniline dyes 

 and various inorganic salts, yield impure spectra. A satu- 

 rated solution of potassium bichromate, which has been 

 accepted as affording yellow light, gives in addition all the 

 red and orange and part of the green. It will be shown 

 later that these individual colors have specific actions on 

 plant growth, hence the light obtained, after passing through 

 bichromate, gives to the plant the combined results of the 

 red, orange, yellow and part of the green. Aminoniacal 

 copper sulphate, if the solution be too dilute, lets through 



