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DEVELOPMENT OF PLANTS 



195 



70. Order d. Siphonales or Tubular Green Algae.-— This 



order Includes a lari^^e number of odd forms that are Idamentous 

 in character and they differ from al^ae previously noterl in that 

 the filaments contain numerous nuclei, but with rare exceptions 

 no cell partitions. Such plants are called coenocytes. They 

 assume various forms and often resemble a small plant with stem, 

 root and leaf, but in all these cases the plant is essentially a huge 

 cell or tube without partitions and containing numerous nuclei. 

 Most of the Siphonales are marine, but one genus, Vauchcria, is 

 well represented in shallow streams, damp places and on the 

 earth of flower pots in greenhouses, where it forms rather coarse 

 green felt-like masses. The plant body consists of long tubular 

 threads, often branching and anchored to the ground by colorless 



Fig. 113. Structure and asexual reproduction of Vaucheria: A, portion 

 of a plant showing the branching tubular filament and colorless root-like 

 outgrowth, r, B, end of a filament enlarging to form a zoospore. C, zoospore. 

 D, germination of a zoospore. 



outgrowths (Fig. 113, A). The protoplasm forms a thick lining 

 layer on the inner wall of the filament and embedded in it are 

 numerous minute chloroplasts, nuclei and oil drops. A water\- 

 cell sap fills the center of the tube. Partitions onl>- appear when 

 reproductive bodies are formed or to close 1 wdimd in (.isc of 



