Vaucheriacece 111 



are sluggish in their movements and continue active for about 

 fifteen minutes. On coming to rest the cilia are at once withdrawn 

 and a cell- wall is developed. Klebs 1 states that zoogonidia can 

 always be produced when filaments which have been kept moist 

 for some days are soaked with water, or when they are removed 

 from a dilute nutritive solution into pure water. The zoogonidia 

 germinate almost immediately by the protrusion of one or more 

 tube-like filaments, one at least of which attaches itself to the 

 substratum by a colourless branched hapteron (or 'rhizoid'). 



Under unfavourable circumstances, particularly if the plants 

 are liable to become dried up, asexual spores of another kind are 

 sometimes developed. The end of a filament swells up into a 

 more or less globular form and then a transverse wall appears and 

 cuts this portion off. Such a spore may rest a considerable time 

 before germination. 



Sometimes, owing to drought, certain filaments break up into a 

 number of distinct ccenocytes, each of which develops a thick cell- 

 wall. These are of the nature of rudimentary gemmae or cysts 2 . 



Sexual reproduction takes place by oogonia and antheridia, and 

 amongst the Siphonese this family of Algse stands alone in the 

 possession of sharply differentiated sexual organs. These are 

 developed at scattered intervals along the cylindrical filament. 

 Except in the dioecious plants the antheridia and oogonia usually 

 arise side by side on the same filament, or they are differentiated 

 portions of a short lateral branch. 



The oogonia usually arise as lateral outgrowths of the filament, 

 or at the end of a very short branch, and they soon assume a more 

 or less rounded or ovate form, being ultimately cut off by a septum 

 at the base. The apex of the oogonium generally develops a 

 rostrum or beak, which is usually turned to one side, either towards 

 the antheridium or away from it. The protoplasm of the oogonium 



1 Klebs, 'Die Bedingungen d. Fortpflanzung bei einigen Algen u. Pilzeti,' Jena, 

 1896. 



2 Bennett and Murray in their 'Handbook of Cryptogamic Botany,' London, 

 1889, p. 284, in referring to this special type of asexual reproduction in Vaucheria, 

 state that "in this condition it was formerly described as a distinct organism under 

 the name of Gongrosira." Dr Scott, also, in his ' Introd. to Structural Botany, 

 Part it,' London, 1897, remarks that "this is called the Gongrosira state, because 

 specimens of Vaucheria in this condition used to be placed in a different genus 

 under that name." These are most unfortunate statements, as Gongrosira is a 

 well-established genus of the Chsetophorales, which reproduces itself asexually by 

 minute biciliated zoogonidia, and none of the plants of which approach in size even 

 the smallest known species of Vaucheria. 



