TAXONOMY 241 



plant is rejuvenated by the formation of an auxospore. This may 

 be formed with or without the conjugation of two parent-protoplasts. 

 In either case the auxospore resulting undergoes a resting stage after 

 which it develops new valves. The newly formed diatom is then 

 several times the size of the individual or individuals which con- 

 tributed to its formation and is endowed with renewed vigor for 

 growth and division. 



6. Order Siphonales (Siphon Alga). This group is characterized 

 by the peculiarity that the organisms constituting it possess proto- 

 plasm containing myriads of nuclei within a common filament or 

 cell cavity not segmented by cell walls. The term ccenocyte has 

 been given to such structures which consist of a many-nucleated mass 

 of protoplasm surrounded by a cell wall. Some of the siphon algae 

 reproduce by zoospore formation, others by conjugation as well as 

 zoospore formation while Vaucheria, the green felt, stands out alone 

 in reproducing both by the formation of a single zoospore and 

 by the production also of ob'gonia and antheridia with resultant 

 fertilization. (Fig. 113). 



7. Order Chorales (The Stoneworts). Family Characeae. The 

 highest group of algae, possessing forms which are differentiated into 

 stems, leaves and rhizoids. 



Char a, a type of this family, is a submerged fresh- water plant 

 which fastens itself to the muddy bottom of ponds, ditches and slow 

 streams by means of slender filaments called rhizoids. From these 

 there arises a many noded (jointed) stem which bears whorls of 

 slender green leaves at its nodes. Branches are also found issuing 

 from some of the nodes which duplicate in appearance the main 

 stem. Reproduction is either asexual or sexual. Asexual repro- 

 duction is accomplished by means of tuber-like bodies borne on 

 submerged parts or by special branches which form rhizoids on their 

 lower nodes and later become separated from the parent plant. 

 Sexual reproduction is effected through the formation of oogonia 

 (female sex organs) and antheridia (male sex organs). These in 

 some species are borne on the same plant; in others, on different 

 plants. In all cases the sexual organs are produced at the nodes. 

 The oogonium develops within itself a large ovum or egg. The 

 antheridium produces within its wall numerous motile sperms. 



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