HOW TO KNOW THE FRESH-WATER ALGAE 



207a Chloroplasts nearly parallel, only slightly twisted; conjugation 

 without the formation of tubes. Fig. 146 S1ROGON1UM 



Fig. 146. Sirogonium sticticum (Engl. Bot.) 

 Kuetz., showing parallel chloroplasts. 



This genus is differentiated from Spirogyra 

 (Fig. 147) on the shape and arrangement 

 (nearly straight and parallel) of the ribbon- 

 like chloroplasts, and (in reproductive ma- 

 Figure 146 terial) by the absence of a conjugation tube 



between the cells of adjoined filaments. 

 There is geniculation of filaments to bring the conjugating cells into 

 juxtaposition. 



207b Chloroplasts definitely spiralled; conjugation by the formation 

 of tubes from one or both cells, either between cells of two dif- 

 ferent filaments (scalariform conjugation), or between adjacent 



cells in the same filament (lateral conjugation). Fig. 147 



SPIROGYRA 



Fig. 147 a, Spirogyra ihizobrachiales 

 Jao, showing rhizoidal branches 

 and conjugation; b, zygospore; c, 

 S. aequinoctialis G. S. West; d, cell 

 showing chloroplasts and numer- 

 ous pyrenoids. 



This is the most commonly found 

 member of the entire order of Zygne- 

 matales. There are numerous spe- 

 cies differentiated on the morpholo- 

 gy of the zygospore, number of chlor- 

 oplasts, and size. Chloroplasts alone, 

 and size of cell do not distinguish 

 species in this genus, and identifi- 

 cation of vegetative material cannot 

 be made. Spirogyra forms green 

 'clouds' of cottony growths, usually 

 in guiet water. In the reproductive 

 state the plants appear at the sur- 

 face, forming cottony mats ('pond scums') and become brown or 'dirty' 

 colored. 



Figure 147 



95 



