MARINE ALG OF BEAUFORT, N. C. 461 
in conspicuous roundish or ellipsoidal sori, scattered over both surfaces; oogonial sori 
black, antheridial sori whitish. 
About 37 species in warm and temperate seas, one extending to Scandinavia. 
Dictyota dichotoma (Hudson) Lamouroux. PI. XCIV, figs. 1, 2c and d, and 3. 
Ulva dichotoma, Hudson, 1762, p. 476. 
Dictyota dichotoma, Lamouroux, 1809, Pp. 42. 
Dictyota dichotoma, Harvey, 1852, Pp. 109. 
Dictyota dichotoma, De Toni, 1895, p. 263. 
P. B-A. Nos, 282, 1641, 2175. Fasc. E. No. CKX. 
Frond erect, flat, ribbonlike, sometimes narrowed at the base to a very short stipelike portion, 
attached by a small, padlike thickening; regularly dichotomous, sometimes with irregular branches 
given off from the apices and from the margins; margins smooth, entire; apices usually rounded, obtuse, 
sometimes rather acute; tetrasporangia, and oogonial and antheridial sori scattered all over both surfaces 
except base, tips, and margins; tetraspores produced continuously, not in regular crops; oogonia and 
antheridia produced in crops at regular intervals; sexual and asexual plants showing a regular alternation 
of generations. 
Reported from warm and temperate waters generally, extending in Europe as far north as Norway 
and Helgoland. 
Very abundant on Fort Macon and Shackleford jetties, Beaufort, N. C., and in harbor from low 
water to 1 m. below Jow water, and occasionally abundant on Bogue Beach, June to October; fairly 
abundant in Newport River near ‘‘Green Rock’’; abundant in North River off Lennoxville and Mar- 
shallburg; one small mass floating in Core Sound off Davis Island; two plants 2 cm. long on coral reef 
off Beaufort, N. C., May, 1907, and fairly abundant, August, 1914 and 1915. Abundant in sound near 
Moores Inlet, Wrightsville Beach, N. C., July to September, 1909. 
This is the northern known limit in North America of the species and of the genus. 
The species varies considerably in size, width, amount of branching, and acuteness of apices, vary- 
ing from plants 1 to 3 mm. wide and 6.5 cm. long to plants 4 to 16 mm. wide and 29 cm. long. ‘The 
average of six well-developed plants from Beaufort was 4 to 12 mm. wide, 18cm. long. The branching 
may be frequent, forming a short, dense habit, or may be infrequent, forming a long, open habit. ‘The 
apices, while usually obtuse, may be acute. The Beaufort plants, while varying in these respects, 
show less variation than English specimens. 
All the specimens of this species dredged from the coral reef, August, 1914, were very narrow and 
finely divided, with numerous almost linear proliferations (Plate XCIV, fig. 2 c and d). 
Plants from unfavorable situations are narrow, often spirally twisted, and usually small. The 
apices of these plants are often acute. Some apices of larger plants may be acute at times, since, when 
conditions are changed to less favorable ones or sometimes after fruiting, there are formed narrow pro- 
jections from the apices. These may widen out later or may grow out as proliferations from the apices, 
later widening out and branching dichotomously. Plants collected at the beginning of this process, 
if examined by themselves, would often be determined as D. bartayresiana Lamour. Under different 
conditions of growth plants may resemble D. bartayresiana Lamour., D. divaricata Lamour., D. dichotoma 
f. latifolia (Kuetz.) Vimassa, f. attenuata (Kuetz.) Vinassa, or f. implexa (Lamour.) Vinassa. ‘These 
three last-named forms are at Beaufort only growth forms occurring under different conditions in the 
environment. D. bartayresiana can itself not be sharply distinguished from D. dichotoma, since 
specimens of these species may overlap. Many specimens of D. dichotoma from England are narrower 
and more acute at the apices than shown in photographs of the type of D. bartayresiana. 
D. dichotoma, wherever carefully observed, has been found to produce its sexual cells in regular 
periodic crops. In the three European stations where this process has been studied—Bangor, Wales, and 
Plymouth, England (Williams, 1905), and Naples, Italy (Lewis, 1910)—the plants produce two 
crops a month at regular intervals related to the tidal seasons, the relations of the crops to the tides 
varying in the different localities. At Beaufort (Hoyt, 1907), only one crop a month is produced, this 
being initiated from three days before up to the day of the greatest springtide at the time of the full 
moon, as shown by the tide tables, and being liberated from three to six days after the day of the greatest 
springtide. Therelation between the greatest springtide and the times of initiation and liberation of the 
