CYANOPHYCE& 437 



(Bzl), Amphithrix (Ktz.), Dichothrix (Zanard.), Sacconema (Bzi.), 

 Brachytrichia (Zan.), and Polythrix (Zan.), the last being marine. 



Hansgirg (Bot. Centralblatt, xxii. and xxiii., 1885) considers the 

 genera ordinarily placed under Rivulariaceae as being higher develop- 

 ments of organisms belonging to the Oscillariaceae. 



LITERATURE. 



De Bary Flora, 1863, p. 577. 

 Bornet and Thuret Notes Algol., fasc. i., 1876, pp. v.-viii. ; and fasc. ii. , 1880, 



PP- I57-I7S. 



Bornet and Thuret Etud. Phycol., 1878, pp. 1-6. 

 Bornet and Flahault Ann. Sc. Nat., iii. (1886), p. 337; and iv. (1886), p. 341. 



ORDER 3. SCYTONEMACEAE 

 (including STIGONEME.E and SIROSIPHONE^E). 



The Scytonemaceae resemble the Rivulariaceae in consisting of 

 branched filaments, often comparatively stout, enclosed, either singly or 

 in numbers, in a mucilaginous sheath ; but differ from that family in dis- 

 playing no differentiation of the two extremities. The filament termi- 

 nates at each end in a large thin-walled apical cell, by the repeated 

 division of which the greater part of the growth in length takes place. 

 The filaments display no oscillation or other spontaneous motion. The 

 mucilaginous sheath which invests one or more filaments is of consider- 

 able thickness, except over the apical cells, where it is very thin ; else- 

 where it is generally lamellated, the lamellae decreasing in number 

 towards the apex, which gives the appearance of a number of funnels 

 inserted one in another. It is often coloured by a deep yellow or brown 

 pigment known as scytonemin, and becomes dry and pulverulent with 

 age, Jbut in younger filaments the sheath is sometimes altogether wanting. 

 The filaments are not septated laterally, but the contents are divided 

 into * gonids ' or pseudocysts, of a spherical or elliptical form, and arranged 

 in a single row in the thinner, often in two parallel rows in portions of the 

 thicker, filaments. These pseudocysts are at first green, but frequently 

 become subsequently dark brown ; and the filament exterior to the 

 pseudocysts is commonly filled by endochrome coloured brown by 

 scytonemin ; the entire plant being therefore distinguished by its brown 

 or orange colour. In Tolypothrix (Ktz.) and Plectonema (Thur.) the 

 filaments generally retain permanently a green colour. 



The Scytonemaceae' may multiply by the individual filaments, 

 enclosed in a common sheath, which have no genetic connection with 

 one another, escaping separately from their sheath, and then investing 

 themselves in a new mucilaginous envelope. But the ordinary mode of 



