272 VAT7CHERIA. 



refractive oil-drops, stained red by alkanna. No starch 

 is present ; the filaments are normally devoid of cross- 

 walls except where a reproductive organ (zoogonidangium, 

 antheridiuin, oogonium) is formed. 



388. Asexual Reproduction by means of Zoogo- 

 nidia. If material which is producing zoogonidia be 

 placed in saucers or other vessels and observed from time 

 to time, numerous young plants will be seen, some float- 

 ing on the surface, others attached to the saucer; these 

 have arisen from germinating zoogonidia. 



To watch the development of zoogonidia, keep the 

 culture in darkness and examine next morning. Some 

 filaments are seen, even with the naked eye or a lens, to 

 have swollen and dark-green tips. Mount some of these 

 filaments in water ; in some cases there will be seen simply 

 the swollen tip, with dense contents surrounding the 

 vacuole, in others the tip will be cut off by a transverse 

 wall, and in others again the zoogonidangium thus 

 formed will be empty. 



Place some of this material in alcohol, and stain it 

 when decolorised. Note that after the formation of the 

 septum which cuts off the gonidangium, the contents 

 become rounded off to form an ovoid or nearly spherical 

 mass, with transparent outer (ectoplasm) and densely 

 granular inner (endoplasm) protoplasmic layers, and a 

 large central vacuole ; the ectoplasm may be radially 

 striated, and staining shows that it contains numerous 

 nuclei, while the denser endoplasm contains chloroplasts. 

 The rounded off zoogonidium finally escapes by rupture 

 of the gonidangium wall near the tip, swims through the 

 water with a rotating movement, and after a short motile 

 period of ten to fifteen minutes it settles down, acquires 

 a wall, and germinates to form a new plant, sending out a 

 green filament and a colourless one (rhizoid). 



Watch a zoogonidium which is moving slowly or coming 

 to rest, and note the numerous cilia ; add iodine, which 

 kills the zoogonidium, and note that there is no cell- wall, 

 and that the cilia are arranged in pairs the insertion of 

 each pair is exactly opposite one of the nuclei in the clear 



