Fritseli . Studies ou Cyanopliyceae. 213 



(loiiiont: Reclierches sur les euveloppes cellulaires des Nostocacees tila- 

 ineuteuses. (Biül. Soc. bot. de Praiice. Ser. 2. T. X. 1888. p. 204). 



K i icliuer: Schizopliyceae. (Eiigler u. Prantl, Die iiatürl. PÜanzenfam. 

 Tai). 1. Abteil." la. 1898.) 



Kleb.s: Über die Organisation der Gallerte bei einigen Algen und Flagel- 

 laten. (Unters. Bot. Inst. Tübingen. Vol. II. Heft II. 1886). 



Kolkwitz: Über die Krümmungen und den Membranbau bei einigen Spalt- 

 algen. (Ber. Deut. bot. Ges. Bd. XV. 1897. p. 460.) 



Kützing: Phj^cologia generalis. 1843. 



Nadson: Über den Bau des Cyanopliyceen-Protnplasts. TScripta botan. 

 Horti L'niversitatis Imperialis Petropolitanae. T. IV. Fascic. IL 1895.) 

 (German resume.) 



Nägeli: Gattungen einzelliger Algen physiologisck und svstematiscli be- 

 arbeitet. Zürich 1849. 



Wager: The cell-structure of tlie Cyanopliyceae. — Preliminary paper. 

 (Proc. Boy. Soc. London. Vol. 72. p. 401. j 



Descriptioii of tlie fi§:ures ou plate TU. 



ilt was found necessar\' in manj' cases to use high magnitications. — 

 Zeiss's apochromatic 3,0 mm, Apert 0,95 and compensation ej^e-piece 12 or 

 18 being mostly employed. All the tigures were drawn with the help of 

 an Abbe di'awing apparatus. The following Symbols are made use of to 

 denote differeut points in the tigTires; c. s. = cell-sheath; /. /. = inner 

 Investment; e. s. = external sheath; t. s. = transverse septiim: ex = exo- 

 .>pore; en. = endospore; //. = heterocyst). 



Fig. 1 and 2. Small portions of filaments of Anahaena. stained with 

 inethyl blue: the transverse septa are curiously contracted, so as to resemble 

 protoplasmic connections. (>' about 2300.) 



Fig. 3. Two young cells of a species of Xontoc in process of division : 

 llie inner Investment is not indicated, a transverse septiim (f. s.) just 

 appearing and cell-sheath constricted: b Division com])lete: cell-sheath of 

 each cell evident, being separated by the thick colourless transverse septum. 

 (X about 250(J). 



Fig. 4. An ordinary vegetative filament of Änohaena in the unstained 

 condition. The cells are separated by well-marked transverse septa. ( 1450.; 



Fig. 5. Portion of a vegetative filament of Anahaena, stained with 

 lodine. The cells are separated from one another by weU-niarked trans- 

 verse septa {t. .s'.) and the cell-sheaths (c. s.) are seen to be individual to 

 each cell. W'ithin tliese latter is a well-defined inner Investment (/. /.j, con- 

 tinuons with tlie transverse septa. Note that at the lower end, which 

 represents the termiuation of a filament, the cell-sheath extends right round 

 the one end of the cell. (>; 2300 about.) 



Fig. 6. Three spoi'es of Analiaena , showing exospore (cell-sheath) and 

 endospore (inner investment). and separated from one another by a well- 

 marked Space. () ' 1450.) 



Fig. 7. Sporogenous cell of Anabaom with contents in jirocess of 

 Protrusion. The liberated portion i.s surrounded by a new inner investment. 

 whilst tiie outline id' the open end of the cylindrical cell-sheath nins round 

 the approximate ecpiator of the jjrotoplast. (X 1-450). 



Fig. 8. Small portion of the sporogenous lilament of Anahao/a (with 

 almost mature spores); the uppermost cell has the inner Investment pro- 

 duced into a papilla temilnally, which is plainly surrounded by the one 

 end of the cell-sheath. (X 1450;. 



Fig. 9. Division of a cell of Gloeocapsa, showing the transverse septum 

 ;ind the contricted cell-sheath, which is as yet not split. (' about 1600.) 



Beihefte Bot. Coutrall.l. B<1. Will. Al.t. I. Hi-ft 1. 15 



