174 DEVELOPMENT OF VAUCHERIA 



It is very manifest, however, that this single cell or plant is 

 decidedly different from the Ulothrix plant because it cannot 

 develop into the Ulothrix plant, but can only produce zoospores. 

 So we see that there are two generations in the life history and 

 that they differ radically in their natures and possibilities of 

 growth. In higher types of plant life it will be seen that the 

 gametospore tends to develop into a more and more complex body 

 or plant and it will be one of the most interesting features of the 

 work to watch the evolution of this asexual plant. 



The higher members of the Chaetophorales illustrates the same 

 gradual differentiation of the gametes, as has been noted in the 

 motile forms of the Volvocales. The female gametes become 

 distinguishable because of their larger size and shorter period of 

 motility, while the male gametes are small, owing to the large 

 numbers that are found in a cell or because of the small size of 

 the cells in which they are developed. Finally, in several of the 

 genera we find but a single female gamete which remains motion- 

 less in the cell. This condition is very well illustrated in one of 

 the genera of the next order. 



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

 includes a large number of odd forms that are filamentous in 

 character and they differ from all other algae in that the filaments 

 contain numerous nuclei, but with rare exceptions no cell parti- 

 tions. 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, Vaucheria, is well repre- 

 sented 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 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 watery cell sap 

 fills the center of the tube. Partitions only appear when repro- 

 ductive bodies are formed or to close a wound in case of injury 



