MicrotJiamniese 



303 



Isogametes with two cilia are known to occur in several genera, and the 

 gametangia may be formed from any cell, except in Gongrosira, in which 

 they are formed only from the lower cells of the thallus. From 6 to 16 

 gametes arise in a gametangium in Endoderma, but they are much more 

 numerous in Gongrosira and Leptosira. In the latter they fuse by their 

 posterior extremities, forming first a spindle-shaped ' zygozoospore,' which 

 then becomes a resting zygote. 



Fig. 197. AC, Microthamnion Kut zing ian urn Nag., youug developing plants, x 500. D, small 

 portion of thallus of M. curvatum W. & G. S. West, x 430. E, part of thallus of M. strictis- 

 simum Rabenh. , x 500. 



The genera are : Microthamnion Nageli, 1849 ; Chlorotylium Kiitzing, 1843 ; Gongrosira 

 Kiitzing, 1845 [ = Stereococcus 1 as described by Wille, 1909; Pilinia Kiitzing, 1843; 

 Ctenocladus Borzi, 1885]; ? AcroUaste Reinsch, 1879; Endoderma Lagerheim, 1883 

 [ = Periphlegmatium Kiitzing, 1843 (in part) ; Entodadia Reinke, 1879 ; Epicladia Reinke, 

 1879] ; Leptosira Borzi, 1885 ; Trichophilus Weber van Bosse, 1887 ; Chlorodonium Borzi, 

 1895 ; Pleurothamnion Borzi, 1895 ; Sporodadus Kuckuck, 1897 ; Glceoplax Schmidle, 



1 The generic name ' Stereococcus' Kiitzing (in Linnaea, viii, 1833, p. 379) was discarded by 

 him (Kiitzing, Phycol. gener. 1843) when he found that it had been given merely to an aggregation 

 of crystals of lime. Vide Nordstedt in Botaniska Notiser, 1911, p. 263. 



