CYANOPHYCEM 



only temporary duration ; when it 

 disappears it leaves the membra- 

 nous sheath open at the extremity. 

 This is especially well seen in 

 Calothrix (Ag.). 



The ordinary mode of multi- 

 plication of the Rivulariacese is 

 by means of hormogones, frag- 

 ments of the green portion 

 which become detached from the 

 rest of the filament, escape from 

 the gelatinous envelope, move 

 about with a creeping motion, 

 eventually come to rest, invest 

 themselves with a gelatinous 

 sheath, and develop into a new 

 filament in which the differenti- 

 ation of the basal and apical 

 extremities is soon manifested. 

 The formation of hormogones 

 is confined to the lower and 

 central portions of the filament, 

 and commences only after the 

 disappearance of the terminal 

 hyaline hair. They vary greatly 

 in length, being composed of 

 from two to fifty pseudocysts. 

 When fully formed, they glide 

 slowly out of the sheath, seyeral 

 often attached to one another. 

 At the period of detachment of 

 the hormogones the whole fila- 

 ment displays a slow movement ; 

 otherwise it is quiescent, the 

 power of motion which in the 

 Oscillariacese belongs to the entire 

 filament being in the Rivulariaceae 

 restricted to the hormogones. 

 Beck (Verhandl. zool.-bot. Gesell. 

 Wien, 1886, p. 47) describes a 

 peculiar mode of formation of the 

 hormogones in Gloeotrichia natans, 



Fig. "i^i,.— Calothrix crusiacea 1 

 (After Bornet.) 



