ZYGNEMACEJE. 83 



Zygnema insigiie. Kutz. Tab. v. t. 17, /. 1. 



Sterile cells equal, or twice as long as broad. 



Copulation scalariforai or lateral ; zygospore globose or 

 slightly oval; membrane brown, even. 



SJZE. Cells 026--03 mm. diam. ; zygospore about '026 x 

 032 mm., or globose about '03 mm. diam. 



De B;iry Conj. p. 78, t. 8, f. 14-16. Rabb. Alg. iii. 249. 

 Kutz. Tab. v. t. 17, f. 1. Kirsch. Alg. Schl. p. 125. 



Tyndaridea insignis, Hass. Alg. p. 163, t. 38, f. 6, 7. Jenner 

 Fl. Tunb. Wells 182. 



Zygnema tenue, Rabli. Exs. No. 674. 



In streams and ditches. 



The cells of this species at the time of conjugation are apt to become 

 much distorted, inflated sometimes on one side, sometimes on the other, 

 and even to conjugate in the manner represented by DeBary, and copied 

 on our plate, 



Plate XXXI. frj. 3. a, sterile cells X 400; b, fertile cells with 

 zygospores X 200 ; c, fertile cells, with longitudinal conjugation, X 200, 

 after De Bary ; d, zygospore X 400. 



GENUS 45. SPXROGYUA. Link. (1820.) 



Cells with one to several parietal chlorophyll bands, usually 

 spirally winding to the right. Copulation ladder-like (Spiro- 

 gyrct) or lateral (Rhynchonema). Zygospores always within the 

 wall of one of the united cells. Copulating cells similar to the 

 sterile ones, or swollen out. 



This genus, as now accepted, includes two genera as recognised by 

 Kutzing, Spirogyra and Mhynehonema. In the former the conjugation 

 was scalariform, and in the latter it was lateral. It is now found that 

 in many species, probably in all, both kinds of conjugation take place, 

 according to circumstances. The same filament, which in some portion 

 of its length conjugates with a neighbouring filament, has also been 

 observed conjugating laterally between two of its own cells. The genus 

 Rhynchonemot therefore has thus been proved to represent only one of 

 the modes of conjugation of the same plant, which under other condi- 

 tions conjugates with a neighbouring filament. 



In past times too great importance was attached to the breadth and 

 length of the cells in the sterile filaments, and also to the character of the 

 spiral bands, features which are now known to be too variable to be relied 

 upon, the most important and reliable characters being derived from the 

 zygospore ; hence only specimens in fructification can be accurately 

 determined. 



The most recent work on the species of Western Europe is a Mono- 

 graph of Spirogyra, as represented in France, by Mons. Paul Petit. 

 (Paris, 1880.) See also Professor Cleve's " Monograph of the Zygnemacese." 



N 



