232 Pennington — A Q hemic o- Physiological 



ing shoots of Elodea. This plant grows easily and rapidly, 

 and furnishes, therefore, a good supply of oxygen. Whether 

 it be this fact or some deeper reason there can be no doubt 

 that Spirogyra grows more rapidly and makes healthier 

 threads when growing with an actively vegetating plant 

 than when growing alone. 



The bowls so stocked were allowed to stand two days in 

 white light before being covered with colored screens in order 

 that possible injurious results from moving the Spirogyra 

 might be outgrown. The bowls were then covered as de- 

 scribed in the previous section of this paper, and placed in 

 windows facing the south and in close proximity to eastern 

 windows, so that they secured the maximum amount of 

 direct sunlight. A greenhouse was found to be too warm 

 to produce the best results. A temperature averaging about 

 22 C. gives the most desirable growth. Occasionally the 

 water was siphoned off and a fresh supply introduced in 

 the same manner. 



When the experiments were begun the cells were in good 

 condition and well supplied with starch. While they con- 

 tinued a record of the temperature and amount of sunlight 

 was kept. The work was repeated many times, the condi- 

 tions, as far as possible, being strictly similar. They ex- 

 tended over an entire winter. The results as given here 

 set forth more especially the chemical, but also, to some 

 extent, the morphological changes which the cells undergo 

 when certain rays only are allowed to act. 



The special changes induced by each colored band will 

 be given separately, the order being that of the colors in 

 the spectrum, beginning with the most refrangible rays. 



Violet. — If the plant be exposed under the violet screen 

 to bright and continuous sunlight, the cells rapidly become 

 abnormal. The first noticeable change-occurs in the chlor- 

 ophyll bands. These, at the end of twenty-four hours, are 

 seen to have a vacuolated appearance, and are of a pale green 

 color. At this time sugar, starch and tannin are still pres- 

 ent in the usual quantity. The protoplasmic pellicle ap- 

 pears normal. 



