284 KJELLMAN, THE ALG^ OF THE ARCTIC SEA. 



Pylaiella nana nob. 



P. thallo macularn miiuitara, diametro 1 mm. in aliis algis formante, e tilis lepentibus, in membranam 

 fere confertis, fila verticalia, cylindrica eraittentibus contexto; zoosporangiis seriatis, gametangiisque saepc ramo- 

 sis, cylindricis vel elongato-conicis fila verticalia terminantibus. Tab. 27, fig. 13 — 17. 



Descriftion. In its vegetative system this alga much i-esembles an Ectocarpus 

 terminalis or E. rejjtans. As in these species the frond i.s formed of branching cell- 

 rows creeping on other alga3, densely corapressed, throwing out at right angles un- 

 branched or very little branched cell-rows. These vertical cell-rows are of three 

 kinds. Some of thein are almost quite cylindrical, composed downwards of cells rich 

 In endochronie, upwards of cells that are poor or altogether wanting in endochrome. 

 Other rows end in organs that resemble the gametangia of Ectocarpi and undoubtedly 

 are of that nature. Those of the third kind ai'e usually slightly claviforni, ending in 

 a simple or branching row of spherical or short tun-shaped cells, which possess a dense, 

 very profuse endochrome. I am not quite clear as to the nature of these roAvs of cells, 

 but they resemble the rows of young zoosporangia in a Pylaiella so much that I cannot 

 but regard them as yet as organs of that kind.. 



The procumbent filaments are composed of cells that in longitudinal section are 

 rectangular, or square, or from five-angular to polygonal, rich in endochrome and with 

 rather thick walls, like the other cells of the frond. The vertical cell-rows issue from 

 the inner part of the disk formed of those densely compact filaments. Those vertical 

 rows which are sterile are about 750 ,w. in length and 15 ,«. in thickness, usually un- 

 branched, composed of cylindrical cells that are from one to one and a half time as 

 long as thick. 



The gametangia are almost always branching, though not much, and elongated- 

 conical, 80 /n. long, 20 — 25 lu. thick. The garnets pass out through a hole formed in the 

 top of every gametangium (fig. 14). The chains of zoosporangia are usually unbranched, 

 composed of from three to more zoosporangia (fig. 15 — 16), sometimes rather much bran- 

 ching. Every branch is formed of one or more zoosporangia, which are different in shape, 

 usually almost spherical, short cylindrical or tun-shaped. Their walls are thicker than 

 those of the vegetative cells. I have not seen zoosporangia with fully developed zoo- 

 spores (fig. 15 — 17). 



If this alga is really a Pylaiella, it is sharply distinguished from all hitherto 

 known species of this genus by its smallness, by the structure of its vegetative system, 

 and the shape of its gametangia. ^ 



Habitat. It grows scattered within the litoral zone in exposed places, epiphytic 

 on Cladophora', and has been found with gametangia and sporangia in August. 



Locality: The Norwegian Polar Sea: Gjesvaar in Finmarken. 



