VAUCHERIA. 143 



nation. If they are rounded, with slender hair-like appendages over the 

 surface, which vibrate and cause motion, they very likely are one of the 

 kinds of reproductive bodies of vaucheria. The hair-like appendages are 

 cilia, and they occur in pairs, several of them distributed over the surface. 

 These rounded bodies are gonidia, and because they are motile they are 

 called zoogonidia. 



By examining some of the threads in the vessel where they occurred we 

 may have perhaps an opportunity to see how they are produced. Short 

 branches are formed on the threads, and the contents are separated from 

 those of the main thread by a septum. The protoplasm and other contents of 

 this branch separate from the wall, round up into a mass, and escape through 

 an opening which is formed in the end. Here they swim around in the 

 water for a time, then come to rest, and germinate by growing out into a 

 tube which forms another vaucheria plant. It will be observed that this 

 kind of reproduction is not the result of the union of two different parts of 

 the plant. It thus differs from that which is termed sexual reproduction. A 

 small part of the plant simply becomes separated from it as a special body, 

 and then grows into a new plant, a sort of multiplication. This kind of re- 

 production has been termed asexual reproduction. 



301. Sexual reproduction in vaucheria. The organs which are concerned 

 in sexual reproduction in vaucheria are very readily obtained for study if 

 one collects the material at the right season. They are found quite readily 

 during the spring and autumn, and may be preserved in formalin for study 

 at any season, if the material cannot be collected fresh at the time it is 

 desired for study. Fine material for study often occurs on the soil of pots in 



greenhouses during the winter. 

 While the zoogonidia are more 

 apt to be found in material 

 which is quite green and fresh- 

 ly growing, the sexual organs 

 are usually more abundant 

 when the threads appear some- 

 what yellowish, or yellow 

 green. 



302. Vaucheria sessi- 

 Us; the sessile vauche- 



Young antheridium and oogonium of Vaucheria ses- -, , . . , 



silis, before separation from contents of thread by a Iia. - 



sexual organs are sessile, 



that is they are not borne on a stalk as in some other species. 

 The sexual organs usually occur several in a group. Fig. 139 

 represents a portion of a fruiting plant. 



