PERIODICITY IN DICTYOTA AT NAPLES 
if. tase Wis 
(WITH ONE FIGURE) 
Periodicity in the production of the sexual cells of Dictyota dichot- 
oma has been described by Wiri1aMs (8) for Bangor, Wales, and 
Plymouth, and by Hoyt (2) for Beaufort, North Carolina. At 
Bangor the sexual products are liberated at fortnightly intervals, the 
rudiments of sexual organs appearing a few tides before the least 
neap, and the mature gametes being liberated 3-5 tides after the 
greatest spring. In October, however, the time relations are reversed. 
At Plymouth the crops are later, as well as slower in maturing, than 
at Bangor, liberation occurring 7-12 tides after the greatest spring. 
At Beaufort only one crop a month is produced, the initiation of 
rudiments occurring the day before, or the day of, and liberation 
taking place six days after, the greatest spring tide. 
These striking differences in the behavior of what is pronounced 
to be the same species in different localities make it desirable that 
careful observations be recorded for this form in other regions than 
those mentioned, and especially in those regions where the tidal 
relations are different. WuLLIAMS surmises that “the periodicity of 
the sexual cells is an hereditary character, and consequently may be 
expected to manifest itself in seas and habitats where there are no 
tides.” OLTMANS (5, pp. 487, 488) states: “Wuttras findet einen 
Zuzammenhang der Entwickelung und Befruchtung und mit den 
bekanntlich in Abstanden von 14 Tagen auftretenden ‘Spring- und 
Nipptiden.’ Da solche im Mittelmeer fehlen, werden erneute 
Untersuchungen hier die Dinge zu klaren haben.” 
With these facts in mind, I took occasion, during March and 
April 1908, to make daily notes on the condition of the sexual plants 
of Dictyota at Naples.t The results of these observations are here 
presented. 
«I take this opportunity of expressing my thanks to the directors of the Smith- 
sonian Institution for the privilege of occupying a table at the Zoological Station in 
Naples, and to Dr. R. Donrn and Dr. Lo Bianco for their cordial cooperation 
during my stay in Naples. 
59] [Botanical Gazette, vol. 50 
