SCinZOPHYTA. 



to simple cell-division. Hormogonia are peculiar fragments of a 

 cell-chain capable of motion, and often exhibit a vigorous motion 

 in the sheath, until at last they escape and grow into a new 

 individual (Fig. 18). The spores are reproductive akinetes 

 (Chamcesiphon, etc.) or resting akinetes ; these latter arise by the 

 vegetative cells enlarging and constructing a thick cell- wall (Fig. 

 19 e/). On germination, this cell- wall bursts and the new cell-chain 

 elongates in the same longitudinal direction as before (Fig. 19 b c). 

 Many {e.g. Oscillaria) may however winter in their ordinary vege- 

 tative stage. Aplanospores are wanting. 



The Fission- Algae are very prevalent in fresh water and on 

 damp soil, less so in salt water ; they also often occur in water 

 which abounds in decaying matter. Some are found in warm 

 springs with a temperature as high as 50 C. 



The Family may be divided into 2 sub-families : 



1. HOMOCYSTE^; (heterocysts are wanting) : Chroococcacece, 

 Lyngbyacece and Chamcesiphonacece. 



2. HETEROCYSTE^ (heterocysts present): Nostocacece, Rivul- 

 ariacece, Scytonemacece and Sirosiphoniacece. 



Order 1. Chroococcaceae. The individuals are 1 many- 

 celled, but all the cells are uniform, 

 united to form plates or irregular 

 masses, often surrounded by a mu- 

 cilaginous cell-wall, but never forming 

 cell-chains. Multiplication by division 

 and sometimes by resting akinetes, but 

 reproductive akinetes are wanting. 

 Chroococcus, Aphanocapsa, Glceocapsa 

 (Fig. 20) , Ccelosphcerium, Merismopeditim, 

 Glaucocystis, Oncobyrsa, Polycystis, Gom- 

 phosphceria. 



Order 2. Lyngbyaceae (Oscil- 

 lariaceae). The cells are discoid (Fig. 21), united to straight or 



spirally twisted, free filaments, 

 which are unbranched, or with 

 spurious branching. The ends 

 of the cell-chains are similar. 

 Heterocysts absent. Reproduc- 

 tion by synakinetes, resting 

 akinetes are wanting. Oscillaria (Fig. 21), Spirulina, Lyvgbya, 

 Microcoleus, Symploca, Plectonema. 



FIG. 20. Glceocapsa atrata: A, 

 B, C, D, E various stages of 

 development. 





FIQ. 21. Oscillaria; a terminal, b central 

 portion of a filament. 



