THE MARINE ALG.E OF NEW ENGLAND. 65 



internal portion consisting of an axial filament formed of a single row 



of rather large cylindrical cells, surrounded by a mass of oblong cells 



sometimes mixed with smaller winding cells; in the spring fronds 



covered with branching hairs, which drop off later in the season; 



unilocular sporangia formed directly from the cortical cells, which do 



not undergo any change in shape or size ; growth trichothallic. 



A small genus, consisting of about fifteen described species, a considerable portion 

 of which bear a close resemblance to D. aculeafa. They are inhabitants of the colder 

 seas in both the northern and southern hemispheres. Our two species are very widely 

 diffused, but D. Ugulata, a common species of California as well as of Europe, is want- 

 ing on our coast. The genus is easily distinguished from its allies by the axial fila- 

 ment and the formation of the zoospores in the unchanged superficial cells. 



D. aculeata, Lamx., Phyc. Brit., PI. 49; !N"er. Am. Bor., Vol. I, 

 PL 4 b. 



Fronds dark olive-brown, one to six feet long, terete . below, com- 

 pressed above, naked at the base ; branches alternate, numerous, long 

 and virgate, lower branches longer than upper, several times pin- 

 nate, clothed in spring with hairs, which fall off and leave alternate, 

 distichous, spine-like processes. 



Common on exposed shores below low-water mark. Throughout the 

 year. Europe. 



A coarse and homely species as usually found ; often washed ashore in large masses. 

 Not likely to be confounded with any other of our species. In spring it presents a 

 feathery appearance, owing to the tufts of hairs with which the frond is beset. It 

 is one of the species used as a fertilizer on the northern coast of New England. 



D. viitiDis, Lam. (Dlchloria viridis, Grev. — Desmarestia viridis, 

 Phyc. Brit., PL 312.) 



Fronds light olive, one to three feet long, cylindrical or but slightly 

 compressed; branches all opposite, distichous, several times pinnate, 

 ultimate branches capillary. 



Common on stones at and below low-water mark. Europe. 



A smaller and much more delicate species than the last, for which it can never be 

 mistaken, rather resembling in some of its conditions a Dictyosiphon. The name is 

 derived from the fact that on decaying or on being placed in fresh water it turns 

 quickly to verdigris-green. Harvey mentions that air-cavities are to be seen in cross- 

 sections of the filaments. The air-cavities are, however, merely the sections of the 

 larger cells which are surrouuded by dense masses of smaller cells, whereas in D. 

 aculeata a cross-section shows the axial filament surrounded by a mass of cells of 

 nearly equal diameter. 



Family DICTYOSIPHONE^. 



Fronds branching, filiform, axis composed of elongated cuboidal cells, 



(he cortex of smaller roundish cells; unilocular sporangia spherical, 



scattered or aggregated, formed from the subcortical cells ; plurilocular 



sporangia unknown. 



S. Miss. 59 5 



