IKKARLING: GROWTH AND REPRODUCTION IN CHARA 485 
relatively little lateral light reaches the plants. When grown 
in battery jars in the laboratory, however, the plants may receive 
light equally from all sides. As to the effects of intensity, it re- 
mains to be tested whether there is a quantitative difference in 
the response. 
Under the conditions of my experiments temperature, within 
the minimum and maximum limits for vegetative growth, did 
not appear to be a primary factor in bringing out the tendency 
to reproduction. It does, however, have a marked effect on the 
rapidity of development of the antheridia and oogonia. In 
only one case, Series A, did the control culture form reproductive 
organs. Yet the controls had the same temperature conditions 
as the other cultures. Under the conditions given the formation 
of antheridia and oogonia can be induced at a temperature as 
low as 2° C. with continuous illumination. With my material 
and conditions the optimum temperature for continuous vege- 
tative growth and gamete production varied between 18° and 
25° C. At a constant temperature over 32° the plants soon 
deteriorated and died. These limits, however, are set only 
tentatively. Further experiments are necessary for definite 
proof. 
It is not certain whether the failure of the eggs in most 
cases to develop into mature oospores is due to the unnatural 
conditions of the experiments or whether it is inherent in this 
particular form of Chara fragilis. This question remains to be 
studied in connection with observations on plants growing in 
nature. Culture o-3 formed an abundance of mature oospores. 
The temperature for this culture was not as high as in the other 
experiments, and the out-of-doors conditions were perhaps more 
closely simulated. It is not clear whether the resulting sterility 
was due to the incompatibility of the gametes or to the abortion 
of the fertilized eggs. 
SUMMARY 
Under the conditions of the experiments described, length 
of day appears to be a primary factor in inducing the formation 
of antheridia and oogonia in Chara fragilis. A few hours of 
artificial illumination in addition to the daylight is sufficient to 
induce the development of antheridia and oogonia in mid- and 
late winter, whereas in nature C. fragilis fruits only from June 
to September, according to Migula (25) and Robinson (30). 
