230 GENERAL BOTANY 



VAUCHERIA (GREEN FELT) 



Various species of Vaucheria, or green felt, are common, either 

 growing on wet soil in greenhouses and on muddy banks or float- 

 ing free with Spirogyra and other algse on the surface of ponds 

 and lakes. The species selected for our immediate study is usually 

 found growing on very wet soil in dense green masses or mats, 

 closely interwoven by the branching of the filaments making up 

 the main portions of the plant body. 



Sexual reproduction. The gametophyte of Vaucheria sessilis is 

 made up of filaments like Spirogyra, but these filaments are 

 highly branched and are not divided by cell walls, so that the 

 entire plant body of an individual plant is composed of one very 

 large multinucleate cell. This long and highly branched cell has 

 the same general structure as that already indicated for adult cells 

 in the higher plants, since it is furnished with a cell wall of cellu- 

 lose lined by a thin cytoplasmic sac, which is kept in place against 

 the cell wall by a huge water vacuole. 



Within the cytoplasmic sac are numerous minute nuclei 

 and small granular chloroplasts, as well as many oil drops, 

 which represent the reserve food of the filament. This struc- 

 ture of the gamete plant of Vaucheria is thus quite unusual 

 among the fresh- water algae in that the plant body, while 

 filamentary and highly branched, is yet composed of a single 

 multinucleate cell. 



The gametangia and gametes (Fig. 120) are formed from 

 specialized branches of the plant body, which arise at irregular 

 intervals along the filaments at the time when sexual repro- 

 duction is about to occur. These reproductive branches at the 

 outset resemble ordinary young vegetative branches, but they 

 soon begin to differentiate (a) into a swollen subspherical 

 female branch and a cylindrical curved male branch. Each 

 subspherical enlargement' becomes filled with very dense cyto- 

 plasm and with many nuclei, which flow into it from the main 

 filament as it increases in size. Sooner or later a transverse wall 

 cuts it off to form a female gametangium (6). In this young 

 gametangium the cytoplasm rounds up to form the female 



