UOO THE PHENOMENON OF 



of the inmost lamella of the cell-membrane in the forma- 

 tion of the reproductive ceU, 



a. With ladder-like {scalariform) yoke-conjugation. 



a. The spore in the connecting canal or middle piece 

 of the double cell. In Zygogonium.* 



j3. The spore in one half of the double cell (in the 

 cavity of one of the tvpo conjugating mother-cells). 

 Ordinarily the case in 8pirogyra,\ and Zygnema.% 



y. A spore in each half. This case occurs only as 

 abnormal in Spirogyra, and appears to depend upon an 

 incomplete carrying through of the conjugation, the 

 union-processes coming into contact, but not anas- 

 tomosing. § 



b. With knee-shaped {geniculate) yoke-conjugation. 



a. The spore in the uniting canal or middle piece. In 

 Mesocarpm. \\ 



j3. The spore (or the gonidium) in one of the halves of 

 the double-cell. Here belong Sirogonium,% with a spore 

 formed exactly as in Spirogyra,a.nA the genus Mougeotia** 

 still enigmatical in its mode of reproduction, probably 

 possessing an active gonidium, leaving the mother-cell 

 directly after its formation. 



c. Chainlike {catenate) union of the cells of the same 

 filament. 



a.^The spore in the lateral connecting-canal of the 

 conjugated-cells. This case is not yet known, but it is 



* Vaucber, 'BCstoiie des Conferves,' t. vii, f. 3 — 4; Hassall, 1. c, 

 t. 39. 



f Vaucher, 1. c, t. iv and y; Hassall, 1. c, t. 18, 25, and 27—32. 



J Vauoher, 1. c, t. vi, f. 4; t. viii, f. 1, 2; Hassall, 1. c, t. 38. 



\ Vide Kiitzmg, 'Phyc. General,' t. 15, f. 1, 3, 4, 6 (of Spirogyra 



Hassall, 1. c, t. 42—45. 

 ■ "iJ Hassall, I. c, t. 26. 



** Hassall, (1. c., p. 172,) indeed, asserts that Mougeotia is propagated by 

 zoospores, but gives no furtlier information regarding their formation. 

 Vaucher (1. c., p. 79, t. viii) formed out oiMougeotia the section " conjugees a 

 tubes int^rieurs," and describes the emergence of already elongated many- 

 celled young filaments from the old cells, a phenomenon which may be 

 explained as accidental development of gonidia remaining in the mother- 

 cell. 



