DESMIDS, DIATOMS, AND FRESH-WATER ALG.E. 107 



ing spores are shown in Fig. 86. The plants are often 

 found in this condition in June and July. 



5. ZYGNEMA (Fig. 87). 



This usually floats unattached. The cells are rather 

 wide and short, the inter- 

 nal stellate masses being a 

 deep green in color. The 



formation of the spores re- 

 Fig. ST.-Zygneraa insigne.. 



sembles that of Spirogyra. 



It is found in conjugation in April. Z. insigne, Fig. 87. 



6. VAUCHERIA (Fig. 88). 



A deep green mat growing on the mud in shallow 

 water, and resembling felt both to touch and sight, will 

 usually prove to be Vaucheria. The filaments are very 

 long, with few branches. The green matter is diffused 

 over the cell- wall, and when the latter is broken, flows 

 out and often forms green globules. The spores are 

 produced in two ways, both of which the beginner will 

 see, as they are not rare early in the season. In one 

 the end of a filament enlarges and becomes club-shaped, 

 while a partition grows across it near the handle of the 

 club. The contents of this new cell become very dark, 

 opaque, and hardened. The free end of the cell then 

 breaks, and the spore slowly passes out, being squeezed 

 into an hour-glass shape as it does so. No sooner is it 

 free than it is off like a flash, being covered by cilia. 

 But it soon settles down, and finally develops into a fil- 



