484 KaRLING: GROWTH AND REPRODUCTION IN CHARA 
cultures were cleaned and fresh water added. The growth from 
that time to November 6 was about 6 cm. A few antheridia 
and oogonia appeared on the new growth. 
It is apparent from these results that a relatively long daily 
period of illumination is necessary to initiate the process of sexual 
reproduction in Chara fragilis in the spring months. The limit 
of the most favorable illumination period has not been deter- 
mined, but it apparently falls beyond twelve hours. 
SERIES G 
olmcted from (ae pare Ondo is iis. ei es March 19 
Grown in south window of laboratory.................. March 1t9-May 7 
' The great sensitiveness of these reactions to light is suggested 
by the record of three cultures growing in a south window of 
the laboratory. These cultures were started on March 19 and 
had the same temperature conditions as Series B and D. About 
50 feet across from this window was a building with windows 
generally lighted as late as 11 p.m. This light was sufficiently 
intense to enable a person to read coarse print at the window 
where the cultures were standing. The reaction to this diffuse 
light was quite striking. On Aprii 15, twenty-six days after 
the cultures were started, antheridia and oogonia appeared. 
In view of the results of other cultures like A, B, C, D and E, 
where an intensity of illumination of only a few foot-candles 
was sufficient to induce sexual reproduction, it seems probable 
that even this diffuse light had an appreciable effect in favoring 
the formation of antheridia and oogonia. 
CONCLUSIONS 
These experiments as noted were started mainly for the pur- 
pose of obtaining material for cytological study. It is apparent, 
however, that the sexual reproduction of Chara fragilis under 
the conditions described is in a considerable degree photoperiodic. 
The occurrence of the reaction is also independent, within a 
certain range, of the intensity of the illumination. These limits 
have not yet been determined, but an illumination of less than 
ten foot-candles was found sufficient under the conditions given 
to induce the formation of antheridia and oogonia in four 
days. Growing at the bottom of ponds and lakes as Chara is 
generally found, the illumination is mostly from above, and 
