130 



Chlorophycece 



great extent on the presence of the Zygnema 1 . Z. ericetorum very rarely con- 

 jugates, and mature zygospores, which are found in the conjugating- tube, have 

 only been observed on one or two occasions. The filaments are 15 22 p. in 

 diameter and the cells often become irregularly thickened. 



Fig. 47. A, Zygnema stellinum (Vauch.) Ag., from Cam Fell, W. Yorks. (x430). 

 B, Z. Vaucherii Ag. var. stagnate (Hass.) Kirchn., from near the Lizard, 

 Cornwall ( x 430). C, Z. ericetorum (Kiitz.) Hansg., from Bombald's Moor, 

 W. Yorks. ( x 415). I), Z. leiospermum De Bary, from Esher Common, Surrey 

 ( x 430), a portion of a filament which was conjugating along the greater part 

 of its length. E, Z. insigne (Hass.) Kiitz., from Malham, W. Yorks. (x330). 

 F, Z. Ealfsii (Hass.) De Bary, from Chippenham Fen, Cambridgeshire ( x 430). 

 ap, aplanospore. 



1 This phenomenon is much more evident in some parts of the tropics, and 

 attention was first called to it by Welwitsch in the ' Journal of Travel and Natural 

 History,' vol. i, 1868. In the damp sandy valley of the Cuanza River, in Angola, 

 the Alga Porphyrosiphon Notarisii occurs in extensive sheets, closely spread like a 



