EXPLANATION OF THE PLATES. 



PLATE XVIII. 



Figs. 1 and 2. Zygnema serratum. The former representing 

 the filaments in its young condition, and showing the spiral 

 disposition of the endochrome; and the latter, the mode 

 of conjugation of the filaments and the sporangia. 



PLATE XIX. 



Figs. 1 and 2. The same conditions of Zygnema orbicu- 

 lare. 



PLATE XX. 



Zygnema alternatum in a state of conjugation. 



PLATE XXI. 



Zygnema interruptum in a similar condition. 



PLATE XXII. 



Figs. 1 and 2. Free and conjugated states of Zygnema 

 nitidum. 



PLATE XXIII. 



Figs. 1 and 2. Zygnema neglectum. Figs. 3 and 4. Zyg- 

 nema deciminum. 



PLATE XXIV. 



Figs. 1 and 2. Free and conjugated states of Zygnema 

 belle. 



PLATE XXV. 



Figs. 1 and 2. The same conditions of Zygnema pellucidum. 



PLATE XXVI. 



Figs. 1 and 2. Conjugated states of Zygnema curvatum. 



