CONFERVOIDEsE ISOGAMAZ 



277 



reproduction have as yet been detected. 

 They are distinguished by the remarkable 

 development of their rhizoids or organs of 

 attachment. 



LITERATURE. 



Wittrock On the Development and Systematic 

 Arrangement of the Pithophor<xce0e, 1877. 



ORDER 3. ULOTRICHACE^E. 



This small order includes the genera 

 Ulothrix (Ktz.), Hormiscia (Aresch.), and 

 perhaps one or two others, not uncommon . 

 in fresh and occasionally in brackish water. 

 The life-history of U. zonata (Ktz.) and 

 other species has been investigated by 

 several observers. They exhibit consider- 

 able affinity both to the Confervacese and 

 to the Hydrodictyeas. Each individual 

 is composed of an unbranched filament of 

 short cells, broader than long, and nearly 

 uniform in length. Some of the cells are 

 megasporanges, giving birth to 2, 4, or 8 

 megazoospores with 4 cilia; others are 

 microsporangesmgametanges, producing 16 

 or 32 biciliated microzoospores or zooga- 

 metes. From the non-sexual megazoo- 

 spores to the zoogametes there is, however, 

 a gradual transition, the only constant dif- 

 ference between them being the number 

 of cilia. Those microzoospores which do 

 not conjugate, as well as the megazoo- 

 spores, germinate directly, germination 

 sometimes taking place even within the 

 mother-cell. Their escape is, however, 

 sometimes arrested, when they lose their 

 cilia, invest themselves with a thick cell- 

 wall, and assume a palmelloid condition. 

 The plants which spring from the germina- 

 tion of the megazoospores are larger than 

 those which spring directly from the micro- 



(After w i"rock.) 



