132 Chlorophycece 



necessarily present at the extremities of every cell in the filament. 

 The nucleus is situated in the central portion of the cell and the 

 protoplasm in which it is embedded is connected with the lining 

 primordial utricle by numerous delicate strands. Many of these 

 strands reach the lining protoplasm exactly opposite a pyrenoid, 

 and as the starch formed during carbon-assimilation makes its 

 appearance round the pyrenoids, this fact has been brought forward 

 as a reason for supposing the nucleus to have a direct function in 

 starch-formation. The nucleus is often clearly visible in living 

 specimens, particularly of 8. majuscula Kiitz. and S. pellucida 

 (Hass.) Ktitz. Mitotic division has been observed in this nucleus 

 by Mitzkewitsch and by C. van Wisselingh, and Gerassimoff has 

 observed cells with either a compound nucleus or two ordinary 

 nuclei. 



The chloroplasts are the most striking feature of Algae belonging 

 to this genus. They are disposed in the primordial utricle in the 

 form of spiral bands, and they vary in number from one to about 

 six or seven in each cell. In some species they are coiled into 

 very close spirals, but in others they are practically straight and 

 longitudinal ; in some, as in S. neglecta (Hass.) Kiitz., their margins 

 are quite smooth and there is a regular axile series of pyrenoids ; 

 in others, as in 8. nitida (Dillw.) Link or 8. porticalis (Vauch.) 

 Cleve, the spiral bands are very broad, with serrated margins and 

 scattered pyrenoids. Between these two extremes there is every 

 gradation, and the character of the chloroplasts always remains 

 constant for any particular species, even though the number of 

 them may vary in different cells of the same filament. It has been 

 ascertained by Kolkwitz 1 that the chloroplasts grow in length in 

 the direction of the coils by both apical and intercalary growth ; 

 and therefore, as this is obliquely to the surface of the cell-wall, 

 there is a gliding motion of the spiral bands through the primordial 

 utricle. 



The coalescence of the gametes takes place in all cases in the 

 female gametangium, which often swells up to twice its normal 

 size. The zygospores may be globular, ellipsoidal, cylindrical with 

 obtuse ends, or they may more rarely assume the form of 

 flattened discs ; and the middle coat of the zygospore is frequently 

 ornamented with distinctive markings. 



1 Kolkwitz in Festschr. f. Swendener, 1899, pp. 271287. 



