92 KJELLMAN, THE ALGjE OF THE AKCTIC SEA. 



show plainly that the plant is attached at first to some hard object, although after- 

 wards, at least in certain cases, it detaches itself and lies free on the bottom. The 

 frond has a short, either flattened and upwards broadening, or extremely short and 

 almost terete, mainstem, from which there issue repeatedly palraately branching branch- 

 systems, spreading like a fan almost in one plane. These are also situated in the 

 same general plane, in consequence whereof the plant gets the appearance of a low, 

 flat bush. The branch-systems contain axes of at least four degrees, all of which, 

 except the ultimate ones, are downwards almost terete, but upwards at the branching- 

 point strongly triangularly expanded; fig. 1. The branch-systems are sometimes almost 

 free, as is shown by the above-quoted figure, sometimes, in older specimens, more or 

 less confluent with one another. It even happens, that branch-systems belonging to 

 different individuals growing close to one another, become confluent. The tips of the 

 branches, except when they are on the point of dividing, are scarcely enlarged, but 

 rounded, or almost truncate. 



The structure of the frond. In this respect the plant coincides so closely with L. 

 soriferum, that I need not enter into any detailed description. The figures 3, 4, 5, 

 6, 7 exhibit the structure bette-r than words could do, and on comparing them with 

 the corresponding figures of L. soriferum, the similarity of the two species in this re- 

 spect is easily perceived. They agree even with regard to the size of the cells. In 

 the cup-shaped layers of tissue on a thin median section the cells are 6 — 10 f*. thick 

 and 20 /u. long at the most. 



Organs of propagation. Conceptacles of sporocarpia and sporangia are to be found 

 on the same individual and on the same branch. They are thinly scattered on and 

 below the tips of the branches (fig. 2) and differ very much in shape from each other. 

 The conceptacles of the sporocarpia present the form of acute cones, upwards traversed 

 by a canal. The conceptacles of the sporangia are flatly hemispherical, about 0,5 /«. in 

 diameter at the base, larger and more elevated than in L. soriferum. They are never 

 found to have grown down into older portions of the frond, which proves the growth 

 of the frond to take place in the same manner as in the preceding species. The roof 

 of the conceptacles of sporangia is intersected by numerous canals, generally 6-sided 

 in transverse section, which are filled with a gelatinous substance and whose orificial 

 cells differ somewhat in shape from the other surface-cells of the roof. The sporangia, 

 fig. 8, are tetrasporic, considerably larger than in L. soriferum, about 250 ,u. long and 

 100 /u. thick, cylindrical, cylindrically spindle-shaped or cylindrically claviform. 



The relation of the present species to others. Amongst the Lithothamnia that I 

 know, this species stands nearest to L. soriferum, from which it seems, however, to be 

 clearly distinguished by its peculiar ramification, its few scattered conceptacles of tetra- 

 sporangia and its large sporangia. 



Hab. According to the kind communication of Mr M. Foslie, the finder of the 

 species, it grows in 20 fathoms water, and, as it seems, in sheltered places of the coast. 

 Specimens, collected at the beginning of August, have carpospores in development and 

 ripe tetraspores. 



