24 



SCfllZOPHYTA. 



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 ef). On germination, this cell-wall bursts and the new cell-chain 

 elongates in the same longitudinal direction as before (Fig. 19 6 c). 

 Many (e.gr. OsciHaria) 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.S; (heterocysts are wanting) : 

 Lyngbyacece and Chamcesiphonacece. 



2. HETEROCYSTEJI (heterocysts present) : Nostocacece, 

 ariacew, Scytonemacece and Sirosiphoniacece. 



Order 1. Chroococcaceae. The individuals are 1 many- 

 celled, but all the cells are uniform, 



Chroococcaceae, 



Itivul- 



D 



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, ApJianocapsa, Gloeocapsa 

 ( Fig. 20) , Ccelosphaerium, Merism opedium , 

 Glaucocystis, Oitcobyrsa, Poli/cystis, Gom- 

 phosplicfria. 



Order 2. Lyngbyaceae (Oscil- 

 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), Spindina, Lyvgbya, 

 Microcoleus, Symploca, Plectonema. 



Fie. 20. Glceocapsa atrata: A, 

 S, C, D, E various stages of 

 development. 



lariacese). 



FIG. 21. Osi'iVfori'n; n terminal, l> central 

 poitinii of a filament. 



