430 STUDIES IN GENERAL PHYSIOLOGY 
few, are developed in the dark; that darkness does not, how- 
ever, interfere with the development of roots. 
2. It was of interest now to establish which rays of the 
visible spectrum favor the development of polyps. The 
effect of light on plants is known to be very strikingly a 
function of the wave-length. Assimilation and in part the 
formation of chlorophyll are pre-eminently functions of 
the long wave-lengths. The heliotropic phenomena are 
essentially a function of the blue rays. According to Sachs, 
the ultra-violet rays are of special importance in the forma- 
tion of blossoms in certain plants. I have shown that the 
short light-waves are most effective heliotropically in animals 
also. From this, however, no conclusions can be drawn as 
to which rays influence most especially the formation of 
polyps. I therefore studied this subject experimentally. 
Unfortunately, these experiments were hampered because 
no other means of obtaining monochromatic light were at 
my disposal than the use of blue and red glass. I had 
special boxes made for these experiments which were painted 
black inside and one wall of which was formed by blue or 
red glass. The dark-red glasses which I employed yielded a 
light which was fairly monochromatic; the dark-blue glasses 
allowed some red to pass through. In the case of the light- 
red and light-blue glasses the light was far from monochro- 
matic. 
Experiment 1.—On August 31 a large number of Euden- 
drium were divided between two vessels, one of which was 
placed in a box in dark-red light, the other in a box in dark- 
blue light. As nearly as I could judge, the red and blue 
glasses allowed about equal quantities of light to pass 
through. The old polyps perished within three days, but 
somewhat sooner in the red than in the blue light. On 
September 4 I discovered the first new polyp in the blue 
light. The number of new polyps in the blue light steadily 
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