VATTCHERIA. 271 



plant may be kept indefinitely in the sterile or vegetative 

 condition either by exposure to bright light in 0*5 per cent. 

 Knop solution which is renewed frequently, or in weak 

 light if this solution is changed very seldom only when a 

 whitish scum appears on the surface. 



387. Structure of Thallus. Place some fresh Yau- 

 cheria on a slide, mount in water, tease out the felted mass 

 gently with needles, and with low power note that : 



(1) The thallus consists of fairly stout green cylindrical 

 branching unseptate filaments, about Ol mm. diameter 

 in the larger species. 



(2) The growing tips of the filaments are colourless 

 and transparent. 



(3) The branching, which may occur sparingly at long 

 intervals, is inonopodial. 



(4) Some branches may develop as colourless rhizoids 

 which enter the soil these are well seen in young plants 

 arising from zoogonidia on germination. 



If no reproductive organs are present, treat the material 

 as directed in 386, in order to induce the development 

 of these organs. Place some of the material in alcohol, 

 to extract the chlorophyll. 



Examine with the high power portions of fresh material 

 mounted in water ; also get ready preparations treated 

 with iodine, irrigated with salt solution, treated with 

 alkannin (or mounted in water and covered for some time 

 with a slice of alkanna root). Also decolorise some 

 material with alcohol, and treat as directed for Spirogyra ; 

 a good fixing solution for Vaucheria consists of 1 gram 

 chromic acid and 8 c.c. glacial acetic acid, dissolved in 

 800 c.c. water. 



In these preparations, note (1) the outer cell- wall; 

 (2) the layer of protoplasm lining the wall ; (3) the central 

 vacuole running through the entire filament. Embedded 

 in the protoplasm layer are (4) numerous oval or spindle- 

 shaped chloroplasts, some of which may be seen in 

 process of division; (5) numerous small nuclei well 

 seen in decolorised and stained specimens; (6) bright 



