MICHIGAN ACADEMY OF SCIENCE. 49 



this point, as the experiments tried were only preliminary, and that 

 phase of the problem has been left until the death-point for certain 

 definite amounts of plant material in a limited volume of the copper 

 sulphate solution shall have been determined. 



Small masses of some filamentous forms of algae were placed in 

 glass dishes in the clear solution of copper sulphate, and some in the 

 same volume of the poison in dishes whose bottoms were partially cov- 

 ered with a thin layer of fine quartz sand, or with garden soil. It was 

 found that the algae lived longer, or lived the same length of time in 

 a much more concentrated solution, in the presence of garden soil than 

 in the clear solution. Sand also tended to lower the death-point, though 

 it was not nearly so effective as the soil. It is a fact of common obser- 

 vation that these low forms are often held at the surface, or even a 

 little above the surface of the water in which they are growing by 

 bnbbles of the oxygen they give off; the gas being held among the fila- 

 ments. Masses containing these bubbles were put in solutions 

 of sufficient quantity and concentration to kill them ordinarily in less 

 than twenty-four hours ; but, being held up above the liquid in a measure, 

 only the cells around the edge of the mass were killed, while the rest 

 lived, and performed their normal functions when returned to pure 

 water. The same was found to be true of Chara. A tip of a branch 

 projecting out of the solution was always found to be alive. 



For convenience, and to have some definite basis upon which to work, 

 portions of Chara plants 10 cm. to 12 cm. in length were used, and 

 these were immersed in 20 cc. of copper sulphate solution of various 

 strengths. In some cases the clear solution was used; in some fine 

 quartz sand was placed on the bottom of the dish; in others a little 

 ordinary garden soil. As yet the effect of varying the quantity of 

 foreign substance present has not been determined. Apparently the 

 amount makes no difference with solutions of the dilutions and small 

 quantities used. Distilled water, tap (hard) water, and river water 

 were tried. The death point was lowest (solution strongest) in all 

 cases in the presence of soil, and highest (died in most dilute solu- 

 tion) in the clear solutions. A curious fact, and as yet unaccounted 

 for, is that the plants lived in a solution of greatest concentration 

 where distilled water was used in making up the solution. One would 

 expect quite the opposite to be true. The plants were always rinsed 

 in some of the solution to be tested before placing them in the 20 cc. 

 A time limit of twenty-four hours Avas set. If, at the end of that time, 

 protoplasm was found to be moving in any part of the plant it was 

 said to be alive. In many instances the plants were removed at the 

 end of twenty-four hours and placed in clear water, and found to live 

 and grow. The problem, then, for this part of the work, might be 

 stated thus : To find out at what dilution 20 cc. of copper sulphate 

 solution will kill 10 cm. to 12 cm. of Chara plant in twenty-four hours, 

 when foreign substances are present, and also when they are not. The 

 following table will show the strength of the solutions necessary as they 

 stand at the present writing. A larger average of results may change 

 it some: 

 7 



