346 



BOTANY 



PART II 



protoplast of which for the purpose of absorbing nourishment loses its cilia 

 and assumes the form of an amoeba ; in this condition it encloses and digests 

 small Algae ("). 



Some marine Peridineae (e.g. Ceratium tripos, Peridinium divergens) are 

 phosphorescent, and play a considerable part in the phosphorescence of the sea (^^). 



Fifi. 250. — Peridineae of tlie plankton. A, Ceratocorys horrida var. nfricana, Indian Ocean (x 250) ; 

 B, Ceratmm tripos interiiicdhm var. aequatorialis, Indian Ocean (x 62); C, Ceratiam tripos 

 gihherum, and 7), Ceratium palmatum, Atlantic Ocean (x 62); E, Ceratium furca, Atlantic 

 Ocean (X 125). (After G. Karsten.) 



Reproduction is by cell-division and also by means of swarm-spores. In the 

 latter case the protoplast escapes from the membrane and either shortly forms a 

 new wall or divides into several swarm-cells (Fig. 258, B). Thick-walled resting 

 cells (cysts) also occur. Zederbauer has recently observed a process of sexual 



reproduction (the conjugation of proto- 

 plasts escaping from two similar cells to 

 form a zygote) in Ceratium {^^). 



Class VI 



Flo. 200. — Spirotacnia condoisata 



Conjug-atae c ^") 



Tliis class of green freshwater 



Algae includes unicellular and 



„ ^ 1- ■, .1 ■ 4. ,. ] .* simply filamentous forms, and is 



gatin;,' cells each divided into two daughter , ^ -^ . . ' 



cells; 2, .3, stages of conjugation :/,, mature clearly (listilict fl'Om that of the 



zygotes. (After archkr ; from oltmanns' Chlorophyccae. The Coiiiusiatae 



■Algae.) ^ f , 1 i. 1 I ..1, 



are most nearly related to the 

 Diatomeae, with which they might be united in the group of the 

 Zygophyceac, since the two classes show essential agreement in their 

 mode of sexual reproduction. This consists in the conjugation of 



