320 KJELLMAN, THE ALGA OF THE ARCTIC SEA. 
Gen. Chlorochytrium Coun. 
Biol. Pflanz, 1,2, p. 102. 
Chlorochytrium Inclusum nob. 
Chl. in statu vegetativo sphzericum vel subsphericum in planta gestatrice omnino inclusum, evolutione 
zoosporarum instante, paullulo prolongatum, depresso-conicum, ampulleforme, ovoideum vel ellipsoideum, demum 
vertice apiculato telam corticalem plante gestatricis penetrante nudum, ostiolo formato zoosporas emittens. Tab. 
Silly eit le 
Description. This alga lives endophytic in Sarcophyllis arctica, being placed in 
most cases near the surface of the nurse-plant, sometimes in the middle of it (fig. 8). 
In its vegetative state it is completely enclosed in the nurse-plant, being covered at 
least by its cortical layer, but sometimes surrounded by its middle layer which is formed 
of branching cell-filaments (fig. 9). It then has a spherical or almost spherical shape, 
80—100 «. in diameter. Its colour is yellowish green. The thin cell-wall is of equal 
thickness. The chromatophore is thin, spread along the whole of the wall. At that 
period when the zoospores are to be produced, the cell is elongated in the direction 
of the nearest surface of the nurse-plant, and becomes ovoid, ellipsoidical, short cone- 
shaped, or bottle-shaped (fig. 12—15). The membrane grows thicker especially at the 
side facing outwards, and there is formed here a short cone-shaped outgrowth of cel- 
lulosa, which contributes probably to the piercing of the cortical layer. The alga 
assumes a more intense yellowish-green colour, the coloured plasma increases in mass 
and is finally divided into a large number of densely packed zoospores. As included 
in the nurse-plant, the alga, both in its vegetative and in its fructiferous stage, pos- 
sesses a greater or less number of different bulgings, evidently caused by the surroun- 
ding tissue impeding its equal growth (fig. 9, 11, 16). The zoospores issue through 
an opening formed by the dissolution of the cell-wall at the top of the cell beyond 
the nurse-plant (fig. 16). As to the structure, germination and further development 
of the zoospores I know nothing, because I have only had the opportunity of exa- 
mining dried specimens. Those individuals which le in the central part of the nurse- 
plant are usually developed to a far greater size than the others. Their longest dia- 
meter can attain even 275 wu. Their membrane is much thickened equally. This may 
possibly be a state of rest which is interrupted when at the dissolution of the nurse- 
plant those individuals are liberated. I have hesitatingly referred the present alga to 
the genus Chlorochytrium, with the other species of which it has much in common. 
The question as to what genus it rightly belongs to, can only be determined with cer- 
tainty, when the history of its development shall be known. 
Habitat. All the specimens of Sarcophyllis edulis that I have examined, at what- 
ever degree of longitude and latitude and whatever season of the year they have been 
taken, have been found to contain a greater or less number of this endophyte. I have 
found it most plentiful and most strongly developed in specimens of Sarcophyllis are- 
tica collected in the winter months, especially in December. It was then so numerous 
as to be counted in hundreds in a couple of square millimeters of the surface of the 
