PERIODICITY IN THE PRODUCTION OF THE SEX UAL 
CELLS OF DICTYOTA DICHOTOMA! 
CONTRIBUTIONS FROM THE BOTANICAL LABORATORY OF THE 
JOHNS HOPKINS UNIVERSITY, No. 6 
Wr DD. Boye 
(WITH TWO CHARTS) 
The antheridia of Dictyota dichotoma (Huds.) Lamour. were 
described in 1855 (1), but the motility of the spermatozoids was not 
discovered until 1896 (2). 
In 1898 Witttams (3) stated that the sexual cells of this alga 
are produced in fortnightly crops bearing a definite relation to the 
tides, and suggested that illumination is the factor determining the 
time of fruiting. In an excellent paper on the cytology of the gameto- 
phytic generation (4) the same author added a few details to his 
previous statements, and in 1905 (5) he gave a full account of the 
periodicity of Dictyota on the north coast of Wales, near Bangor, and 
discussed the factors which may determine this behavior. He also 
recorded a similar periodicity in this alga at Plymouth, England. 
At both places the time of production of the sexual crops bears a 
definite relation to the spring tides. The spring tides are, of course, 
those of greatest range, having the highest floods and the lowest 
ebbs, and occur every two weeks, about the times of the new and full 
moons. The neap tides are those of least range, having the lowest 
floods and the highest ebbs, and occur between the springs. A sum- 
mary of records taken at Bangor for seven years shows that at this 
place the sexual crops of Dictyota dichotoma are generally initiated 
several tides before the least neap, and liberated from three to five 
_ tides after the greatest spring. They thus extend through parts of 
two sets of spring tides. 
In his discussion of the factors which may regulate the periodicity, 
Wittrams assumes that the determining factor is one that varies 
with the alternation of spring and neap tides, and is most marked at 
: An abstract of this paper was presented before Section G of the A. A. A. S., 
New York City, December 31, 1906. 
383] [Botanical Gazette, vol. 43 
