268 S^IEOGTRA. 



plasmolyse but also kill the cell, hence in plasmolysis experiments 

 we use reagents which cause plasmolysis without also causing 

 death. Irrigate a fresh specimen, while watching it under the 

 high power, with some 2 or 3 per cent, salt solution ; as the solution 

 passes through the cell-wall and water escapes by diffusion (osmosis) 

 from the cell-sap in the vacuole, the protoplasm film is forced 

 inwards, and the cell-contents become rounded off. Now draw 

 water through ; as this replaces the salt solution, the cells return to 

 the normal turgid condition. 



Place some fresh material in very strong salt solution ; or simply 

 put some dry salt on a slide, add enough water to dissolve it, and 

 add some fresh filaments. Marked plasmolysis occurs, the cell- 

 contents becoming rounded off to form a ball, while the cell- wall 

 itself becomes folded and crumpled owing to the sudden and 

 complete collapse by plasmolysis. 



384. Conjugation (Fig. 57). Examine material show- 

 ing stages in conjugation ; either collect fresh conjugating 

 material (chiefly found in spring and early summer) or try 

 to induce conjugation in material kept indoors ( 379). 

 Note that 



(1) The cells of two opposite filaments put out rounded 

 projections of their lateral walls. 



(2) These processes meet and fuse at the tips, so that 

 the two opposed cells become continuous by a transverse 

 conjugation tube. 



(3) Meanwhile, the contents of both cells have become 

 rounded off, forming the gametes, this rounding-off 

 occurring earlier and being more marked in one cell (male) 

 than in the other (female) usually all the cells of one 

 filament are " male " and all those of the other filament 

 "female." 



(4) The contents of the male cell pass over through the 

 conjugation tube and fuse with those of the female cell, to 

 form the egg-shaped or rounded zygote. 



(5) The zygote acquires a thick wall, its contents become 

 brownish, and it is now a zygospore. 



Keep conjugated filaments in a vessel of water, and 

 observe the development of the zygospores from time to 

 time ; note that the thick coat is stratified, the outer and 

 inner layers being colourless while the middle layers 

 become brown, also that the zygospore at first contains 



