Studies in the Dictyotaceae. 
III. The Periodicity of the Sexual Cells in Dictyota dichotoma. 
BY 
J. LLOYD WILLIAMS, 
Assistant Lecturer in Botany , University College , Bangor ; 
With six Diagrams in the Text, 
HILE studying the development of the sexual cells in Dictyota the 
V V interesting discovery was made that the process was practically 
simultaneous, not only for a given plant, but for all the plants of the 
locality ; that the crop so produced took but little time to mature and 
become liberated, and that a succession of many of these crops were pro- 
duced during the course of the fruiting season. A closer study enabled 
one to see that each crop was initiated, matured, and discharged all within 
a fortnight, and that a general liberation of the oospheres and antherozoids 
of the locality took place on a certain day, or sometimes two or three days, 
immediately after the highest springtide. 
Although the main facts were put beyond any doubt at an early period 
of the inquiry, there were slight variations in the times of maturation of some 
of the crops, and of particular sori, as well as of occasional plants. These 
deviations from the general rule took a longer time and more careful study 
to account for. Records have been systematically kept of the details relating 
to these crops from 1897 to the present year, and these enable us to come 
to a definite conclusion with regard to the factors concerned in bringing 
about the periodicity, as well as in producing local departures from the 
normal course of events. 
In order to understand the facts, a general description of the sexual 
plant will be useful. Dictyota is an annual. Germlings, and, in all proba- 
bility, small vegetative shoots from the preceding autumn which have 
remained dormant during the winter and spring, commence to elongate 
during May, and here and there fruiting plants may be met with about the 
end of June, but reproduction is not by any means common until the end of 
July. During August and September the process is general and perfectly 
[Annals of Botany, Vol. XIX. No. LXXVI. October, 1905.] 
