COXFERVOIDE.E ISOGAM.-E 



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 Pithophoraceae, 1877. 



Order 3. — Ulotrichace.^. 



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-histor}' of U. zonata (Ktz.) and 

 other species has been investigated by 

 several observers. They exhibit consider- 

 able affinity both to the Confervaceae and 

 to the Hydrodictyeae. Each individual 

 is composed of an unbranched filament of 

 short cells, broader than long, and nearly 

 uniform in len2:th. Some of the cells are 

 viegasporanges. giving birth to 2, 4, or 8 

 megazoospores with 4 cilia : others are 

 microsporanges or game ta?iges, 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, mvest 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- 



.^ 



Fig. 245. — Pithophora Keivensis Wittr., 

 branching plant ; sp, spore (x- 20). 

 (After Wittrock.) 



